Miniaturized, self-sufficient bioelectronics powered by unconventional micropower may lead to a new generation of implantable, wireless, minimally invasive medical devices, such as pacemakers, defibrillators, drug-delivering pumps, sensor transmitters, and neurostimulators. Studies have shown that micro-enzymatic biofuel cells (EBFCs) are among the most intuitive candidates for in vivo micropower. In the fisrt part of this thesis, the prototype design of an EBFC chip, having 3D intedigitated microelectrode arrays was proposed to obtain an optimum design of 3D microelectrode arrays for carbon microelectromechanical systems (C-MEMS) based EBFCs. A detailed modeling solving partial differential equations (PDEs) by finite element techniques has been developed on the effect of 1) dimensions of microelectrodes, 2) spatial arrangement of 3D microelectrode arrays, 3) geometry of microelectrode on the EBFC performance based on COMSOL Multiphysics. In the second part of this thesis, in order to investigate the performance of an EBFC, behavior of an EBFC chip performance inside an artery has been studied. COMSOL Multiphysics software has also been applied to analyze mass transport for different orientations of an EBFC chip inside a blood artery. Two orientations: horizontal position (HP) and vertical position (VP) have been analyzed. The third part of this thesis has been focused on experimental work towards high performance EBFC. This work has integrated graphene/enzyme onto three-dimensional (3D) micropillar arrays in order to obtain efficient enzyme immobilization, enhanced enzyme loading and facilitate direct electron transfer. The developed 3D graphene/enzyme network based EBFC generated a maximum power density of 136.3 μWcm-2 at 0.59 V, which is almost 7 times of the maximum power density of the bare 3D carbon micropillar arrays based EBFC. To further improve the EBFC performance, reduced graphene oxide (rGO)/carbon nanotubes (CNTs) has been integrated onto 3D mciropillar arrays to further increase EBFC performance in the fourth part of this thesisThe developed rGO/CNTs based EBFC generated twice the maximum power density of rGO based EBFC. Through a comparison of experimental and theoretical results, the cell performance efficiency is noted to be 67%.

Recent development in portable electronics and electric vehicles have increased the demand for high performance lithium ion batteries. However, it is still challenging to produce high energy and high power lithium ion batteries. The major objective of this research is to fabricate advanced electrode materials with enhanced power density and energy density. Porous Li4Ti5O12 (LTO) and its nanocomposites (with Si and reduced graphene oxide (rGO)) synthesized by electrostatic spray deposition (ESD) technique were mainly studied and promising electrochemical performance was achieved. In chapter 3, porous LTO thin film electrode was synthesized by ESD to solve the low energy density and low power density issues by providing good ionic and electronic conductivities. Electrochemical test results showed that it had a large specific capacity of 357 mAh g-1 at 0.15 A g-1, which was even higher than its theoretical capacity. It also exhibited very high rate capability of 98 mAh g-1 at 6 A g-1. The improved electrochemical performance was due to the advantage of ESD generated porous structures. In order to further enhance the power density of LTO, ESD derived LTO/rGO composite electrodes were studied in chapter 4. In chapter 5, high energy density component Si was introduced viii into LTO composite. The synergistic effect between commercial LTO and Si powder was studied. Then, ESD derived LTO/Si/rGO composite was prepared and evaluated. At 0.15 A g-1, a stable capacity of 624 mAh g-1 was observed, which was much higher than the capacities of LTO and LTO/rGO electrodes. In addition, effect of activation process on electrochemical performance of carbon nanofibers (ACNFs) and feasibility of ion intercalation into 2D MMT montmorillonite clay (MMT) were studied and discussed in chapter 6. In summary, we have successfully synthesized various LTO based electrodes by ESD. Both high energy and high power density were achieved as compared to commercial LTO electrode. Through electrochemical characterization and charge storage distribution analysis, origins of the high rate capability were proposed. This work demonstrates ESD as a powerful tool for fabricating high performance porous structures and nanocomposite electrode materials.

The goal of this study is to characterize the mixing that occurs in a microfluidic chip. To characterize the mixing, the minimum length to complete mixing and evolution of mixing will be investigated. There are two types of mixing that occur within a microfluidic channel, diffusion and advection. In the beginning of the microfluidic chip, diffusion is the dominant form of mixing, and in the later portion of the microfluidic chip advection is the dominant form of mixing. The type of design used for this experiment was a zig zag geometry microfluidic chip with channel dimensions of 60 µm X 500 µm X 522 mm. The minimum length for complete mixing was 361 ± 3.475 µm at a flow rate of 25 mL/hr. The mixing was measured using optical light microscopy. For all flow rates less than 20 mL/hr the flow rate was too low to mix the two fluids. The pressure produced by the 30 mL/hr flow rate caused the microfluidic chip to fail.

Rice straw is a global and proliferate agricultural waste whose production grossly outstrips viable uses. Current disposal methods are not sustainable, and more convenient methods – such as incineration – exude poor environmental stewardship. Although the direct use of straw bales in building construction presents a practical and sustainable alternative, engineering challenges associated with using it prevent its wide adoption. The Stak Block – a composite formed from compressed rice straw and a heat-cured adhesive – may overcome challenges associated with straw bale building. However, the times and temperatures needed to cure the binder with straw are not well understood. Therefore, the goal of this thesis was to study straw cubes (in lieu of the full-scale Stak Block) to discern a time-temperature relationship. A finite element (FE) model of the Stak Block was created to simulate the heating process. The results of this study indicated that the adhesive may actually cure at temperatures less than 100°C. This data influenced the times and temperatures that binder-treated straw cubes were baked at for the first of several iterations. A chemical dye was used to discern if cubes had cured or not. In addition, mechanical testing was used to inspect cubes for curing and to support the results obtained from using a chemical dye. Results from cubes inspected with the chemical dye method were then used to develop an inverse relationship between time and temperature needed to cure the cubes – with the lowest observed cure temperature to be 65°C for 2 hours and the fastest cure time of 30 minutes at 150 and 125°C. Following the iterative experiments, an FE model of the cube was created and fitted to the results of the iterative experiments. Values for thermal conductivity (k = 0.1 W/m-K)and specific heat (Cp = 2000 J/kg-K) used to fit the FE cube model were applied appropriately to the Stak Block FE model in order to estimate curing times at different temperatures.

ABSTRACT The Characterization and Analysis of In-vitro and Elevated Temperature Repassivation of Ti-6Al-4V via AFM Techniques Aaron J Guerrero Research in the corrosion of orthopaedic implants is a growing research field where implants have been known to show adverse effects in patients who have encountered the unfortunate dissolution of their implants due to corrosion. Once corrosion begins within the body, many adverse biological reactions can occur such as late on-set infections resulting in severe health complications. The focus of this research is specifically related to the problem of late on-set infections caused by localized corrosion of orthopaedic implants. In medical implants today the most common form of corrosion protection is the implant materials’ ability to impede corrosion through the formation of an oxide layer. This ability to passivate and quickly repassivate a uniform and stable oxide layer dictates how well an orthopaedic implant will survive in-vivo. To better understand the repassivation of orthopaedic implant materials, research was conducted at the nanoscale via atomic force microscopy (AFM) on anodized Ti-6Al-4V. Using an Asylum Research MFP-3DTM AFM and AFM lithography techniques, nano scratch test methods were created simulating in-vitro surface repassivation conditions. These nano-scratches were created and characterized in Hank’s balanced saline solution (HBSS) with the AFM in contact mode at 1 and 3 Hz scan rates. HBSS was used as it best simulates the pH, ionic compounds, and constituents that are commonly found in blood. It was discovered that the AFM was successful in creating in-vitro repassivation conditions. However, the ability of the AFM to successfully observe repassivation was limited by the speed of the AFM scanner. Using the same AFM scratch methods, experiments were performed in air and in-vitro and characterized with AFM conductance measurements at 20, 37, & 45 °C. The conductance measurements were taken using an AFM conductance module and allowed for observations of decreasing current measurements over time. The current data was then used to calculate current density, resistivity, conductance, and electron mobility and compared to similar experiments This study highlights the ability of the AFM to create and characterize repassivation and shows promise in developing further capability to use the AFM for characterization of repassivation on the nanoscale. Keywords: Orthopaedics, late on-set infections, repassivation, AFM, lithography, conductive measurements.

The purpose of this study is to improve spacecraft shielding from radiation in space. It focuses on the evaluation of shielding efficiency of different materials. The efficiency of a shield is evaluated by the dose profile within the shield and the amount of dose absorbed by a target using the Monte Carlo transport code called FLUKA. The output of this code is validated by recreating the experiments from published papers and comparing the results. Once the FLUKA’s output is validated, the efficiency of sixteen materials, subject to SPE and GCR sources, are evaluated. The efficiency comparison is made by fixing the area density of a shield. It was found that polyethylene, water, carbon and silicon outperform aluminum – the primary metal used in spacecraft. In case of composite shield, made of layers of different materials, the 3Carb-9Al combination has better performance than the shield made just of aluminum. This holds true for both Solar Particle Events (SPEs) and Galactic Cosmic Ray (GCR). However, the choice of material is more efficient at shielding from SPE particles rather than from GCR. In case of GCR, the choice of materials is found to have rather small effect on the efficiency of a shield. The percent difference between the rate of dose absorption by a target, shielded by different materials, is within about 9%. Secondary particles make a significant contribution to the target’s dose. For SPEs, the secondary particles are primarily electrons and neutrons. For GCRs, the secondary particles are primarily pions, α-particles and electrons. Protons contribute more than 50% to the target’s dose in both cases.

Electrochemical conversion devices are a developing technology that prove to be a viable and more efficient alternative to current environmentally friendly generation devices. As such, constant research has been done in the last few decades to increase their applications and reliability. One of these systems, and the focus of this research, is the single cell Solid Oxide Fuel Cell (SOFC). These systems are a developing technology which main caveat is the need of high operating temperatures and costs. As such, most multidisciplinary research has been focused on researching materials and/or processes that help mitigate the costs or lower the operating temperature. The research presented in this paper focused on the manufacturing of a cubic stabilized zirconia (CSZ) electrolyte thin membrane for a single cell SOFC through tape casting. Thus, the process was divided into slurry preparation, tape casting, further processing, and analysis of samples. First the tape was produced reaching optimal viscosity (between 500 to 6000 cP) and minimizing impurities. Then, the slurry was poured into the doctor's blade with a 200 micrometers gap and allowed to dry. Samples were punched from the green tape with a diameter of 28 inches. Afterwards, these samples were pressed and sintered with a force of 218016 N and temperature of 1550 degrees celsius, respectively. These steps are done to maximize density and grain growth and minimize porosity. Lastly, the tape went further analysis and it was stated that further research should be done to determine this tape viability for stationary SOFC application.

<p>A supply shortage of solar-grade silicon in recent years resulted from a rapid expansion of the solar cell industry. Therefore, many efforts have been done to obtain reliable metallurgical methods for production of SoG silicon from metallurgical grade silicon.</p> <p>In this research, refining of metallurgical grade silicon by chlorination treatment with the emphasis on Al removal was investigated. Thermodynamic calculations through Factsage confirmed the feasibility of Al removal in repeated steps of chlorination. Therefore, an Ar+SiCl₄ gas mixture with different flow rates was applied to the silicon melt by blowing and injection methods at different temperatures and the ICP-OES was used for analysis of the impurities in silicon.</p> <p>Results revealed that Al removal from silicon by chlorination treatment under the conditions employed in this study is first order reaction with respect to Al. By increasing the temperature in the chlorination process, the rate constant increases which is related to an increase in the liquid mass transfer rate. Also the observed higher rates of Al removal under injection conditions appear to be the result of improved stirring in the melt rather than an increase in the interfacial area.</p> / Master of Applied Science (MASc)

<p>Free solidification molecular dynamics simulations were used to study solute trapping behaviour in the Ni-Cu alloy system. The segregation coefficient, K, as a function of crys- tallization rate was compared with several theories of trapping and, in agreement with a model proposed by Sobolev, it was found that complete trapping (K=1) occurs at a finite velocity. In order to gain further insight into the thermodynamic and kinetic factors affect- ing solute trapping, forced velocity phase field crystal (PFC) simulations were performed on a model binary alloy. We find that the complete trapping limit only occurs if a com- bination of wave-like and diffusive dynamics equation of motion of the PFC alloy model. Finally, an amplitude expansion analysis of the PFC formulation for constant velocity so- lidification was performed and an analytic expression for the complete trapping limit and solute drag was obtained.</p> / Doctor of Philosophy (PhD)

Surface integrity of manufactured components has a critical impact on their functional performance. Magnesium alloys are lightweight materials used in the transportation industry and are also emerging as a potential material for biodegradable medical implants. However, the unsatisfactory corrosion performance of Mg alloys limits their application to a great extent. Surface integrity factors, such as grain size, crystallographic orientation and residual stress, have been proved to remarkably influence the functional performance of magnesium alloys, including corrosion resistance, wear resistance and fatigue life. In this dissertation, the influence of machining conditions, including dry and cryogenic cooling (liquid nitrogen was sprayed to the machined surface during machining), cutting edge radius, cutting speed and feed rate, on the surface integrity of AZ31B Mg alloy was investigated. Cryogenic machining led to the formation of a "featureless layer" on the machined surface where significant grain refinement from 12 μm to 31 nm occurred due to dynamic recrystallization (DRX), as well as increased intensity of basal plane on the surface and more compressive residual stresses. Dry and cryogenic burnishing experiments of the same material were conducted using a fixed roller setup. The thickness of the processed-influenced layer, where remarkable microstructural changes occurred, was dramatically increased from the maximum value of 20 μm during machining to 3.4 mm during burnishing. The burnishing process also produced a stronger basal texture on the surface than the machining process. Preliminary corrosion tests were conducted to evaluate the corrosion performance of selected machined and burnished AZ31B Mg samples in 5% NaCl solution and simulated body fluid (SBF). Cryogenic cooling and large edge radius tools were found to significantly improve the corrosion performance of machined samples in both solutions. The largest improvement in the material's corrosion performance was achieved by burnishing. A finite element study was conducted for machining of AZ31B Mg alloy and calibrated using the experimental data. A user subroutine was developed and incorporated to predict the grain size changes induced by machining. Good agreements between the predicted and measured grain size as well as thickness of featureless layers were achieved. Numerical studies were extended to include the influence of rake angle, feed rate and cutting speed on the featureless layer formation.