<p>Superplastic forming (SPF) represents one feasible method to improve the formability of wrought magnesium alloy sheets at high temperatures. A fine grain structure not only improves the ductility but also increases the optimum strain rate thus, reducing the cost of SPF. Microstructural stability of AZ31 sheets have been characterized following different heat treatments. Second phase particles help to suppress grain growth due to the pinning effect. Thus once the temperature exceeds 450°C pmticles dissolve leading to abnormal grain growth. Superplastic behavior based on the fine grain structure of AZ31 was therefore evaluated at temperatures ranging from 200°C to 400°C with constant strain rates of 2.7*10^-4 s^-1 to 8.8*10^-3 s^-1. The dominant defonnation mechanism is grain boundary sliding, accommodated by dislocation creep. Under the current test conditions the initial (12μm grain size) structure is unstable and leads to dynamic recrystallization (DRX). Competition between DRX and grain growth leads to a variation of mechanical response with test conditions. Further grain refinement of AZ31 sheets was investigated through warm rolling tests for both symmetric and asymmetric types at 200°C and 300°C, followed by 200°C annealing. Asymmetric rolling was more effective for grain refinement and achieved better mechanical properties than symmetric rolling.</p> / Master of Applied Science (MASc)

<p>p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Times}</p> <p>Due to the environmental burden of fossil fuel combustion, a major strategic shift towards renewable green sources and environmentally benign power generation technology makes biofuel cells a possible alternative, though their extremely low current density remains a bottleneck for the further practical applications. Recent progress shows some promise to increase the current by platinum (Pt) electrodes, and alkaline solution to replace the enzymes/microbes. However, the approach involves high cost of noble metals as well as their poisoning effect. We report here a glucose biofuel cell based on nickel (Ni) electrodes and alkaline medium without the catalyst poisoning found in Pt systems. Surprisingly, a six-fold current increase over time, and a final current density equivalent to 1.5 times that of Pt have been achieved. They are found to be caused by the transformation of glucose to an enediol form, the expansion of triple phase boundaries where cathode reactions take place, and the enhancement of reaction kinetics by alkaline solution. The results not only provide a dramatic increase in current and overall biofuel cell performance, but also demonstrate a low cost approach to renewable source utilization, if corresponding designs can be implemented.</p> / Master of Applied Science (MASc)

<p>Electrochemical supercapacitors (ES) have become an attractive technology in electrical energy storage devices and found many applications in a number of areas. The development of ES requires fabrication of advanced electrodes with novel materials and new techniques. Conducting polymer polypyrrole (PPy) has been found to be a promising electrode for ES due to its high pseudo capacitance and good electrical conductivity. The polypyrrole based composite electrode with multiwall carbon nanotubes (MWCNTs) has been proved to enhance the electrochemical performance of ES.</p> <p>Anodic electrochemical deposition of polypyrrole film and composite with MWCNTs has been successfully achieved on a stainless steel substrates in aqueous solutions. Novel additives, such as tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) and sodium salicylate have been employed for the electro-synthesis of PPy. The role of additives in the electrodeposition process have been discussed. The electrochemical properties of PPy and PPylMWCNT composite have been investigated and compared by using different characterization techniques.</p> <p>The results showed that good quality PPy film and PPy/MWCNT composite can be obtained on stainless steel without anodic dissolution of anode using novel additives in aqueous solutions. The PPy films provided corrosion protection for stainless steel in aqueous solutions. High electrochemical performance of PPy film was achieved, the electrochemical behavior of PPy electrodes was significantly enhanced when MWCNTs were incorporated into the film matrix. Hence, investigations in this work indicated that PPy and PPy/MWCNT composite deposited on the stainless steel substrates are promising electrode materials for ES.</p> / Master of Applied Science (MASc)

<p>The electrochemical supercapacitors (ESs) are an emerging technology that promises to play an important role in meeting the demands of electronic devices and systems both now and in the future. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. Nanostructured manganese oxides in various forms have been found to be promising electrode materials for ES.</p> <p>Cathodic electrodeposition method has been developed for the fabrication of nanostructured manganese dioxide films. Manganese oxide films were obtained by galvanostatic, pulse and reverse pulse electrodeposition from KMnO₄ solutions. The diffusion-controlled deposition mechanism is based on the reduction of anionic MnO₄^- at the cathode surface. It was shown that film porosity is beneficial for the charge transfer during deposition, crack prevention in thick films and electrolyte diffusion in fabricated ES electrodes. The microstructure, chemical properties and charge storage properties of films prepared by different deposition methods are investigated and compared.</p> <p>Novel chemical precipitation methods have been developed to produce manganese dioxide and Ag-doped manganese dioxide nanoparticles. Composite electrodes for ES were fabricated by impregnation of slurries of the manganese dioxide nanoparticles and carbon black into porous nickel foam current collectors. The microstructure and chemical properties of the powders were characterized. The capacitive behaviour of the composite electrodes was studied.</p> / Master of Applied Science (MASc)

<p>New electrochemical deposition methods have been developed for the fabrication of advanced composite coatings for biosensors applications. The methods are based on electrodeposition of biopolymers, such as cathodic electrodeposition of chitosan, anodic electrodeposition of alginic acid and hyaluronic acid. Another approach is based on electrolytic deposition and electrophoretic deposition of ceramic materials and chitosan. Electrochemical strategies have been discovered for the electrochemical co-deposition of polymers with enzymes, such as glucose oxidase and hemoglobin. Glucose oxidase was used as a model enzyme for the development of new electrochemical strategies for the fabrication of composite coatings for applications in biosensors. New strategies have been further utilized for the fabrication of novel composites containing hemoglobin. It was found that co-deposition of biopolymers and enzymes from the solutions resulted in the fabrication of composite materials which can keep the activity of the enzymes.</p> <p>Electrochemical methods have been developed for the deposition of composite coatings containing ceramic materials (ZnO) in the matrix of chitosan. The composite coatings can be utilized for the immobilization of enzymes by the electrostatic attraction. The composition and microstructure of the composite coatings were investigated. The composition of these nanocomposite coatings can be varied by variation of bath composition for electrodeposition. The deposition yield was studied at various deposition conditions. Electrochemical deposition mechanisms have been investigated and discussed. Obtained results pave the way for the fabrication of novel coatings for immobilization of enzymes and for application in advanced biosensors.</p> / Master of Applied Science (MASc)

<p>The development of new materials with a combination of high strength and ductility is required for the automotive industry, due to the demand for increased fuel efficiency while maintaining vehicle safety and performance. High-Mn steels combine exceptional strength and ductility to achieve the sustained rates of high work hardening required to achieve these objectives. Fe-22Mn-C alloys containing strain-induced deformation products (twins and ε-martensite) contribute to the high work hardening rates by acting as boundaries for dislocation motion. Three Fe-22Mn-C alloys were investigated with varying carbon contents of 0.6, 0.4 and 0.2 wt% and stacking fault energies (SFEs) of 37.2, 33.4 and 29.6 mJ/m² , respectively. Their microstructural evolution and mechanical properties were evaluated.<br /> The as-annealed Fe-22Mn-0.6C alloy comprised an austenitic microstructure, produced twins during deformation and had the highest sustained work hardening rate of the three alloys. The kinematic hardening contribution was due to the production of twins during deformation, adding to the overall flow stress. The flow stress was successfully modeled with contributions from the yield strength, isotropic hardening and kinematic hardening. The main damage mechanism was the separation of grain boundaries and the production of twins during defonnation classified the 0.6C alloy as a TWIP steel.<br /> The Fe-22Mn-OAC alloy displayed an austenitic matrix ill the as-annealed microstructure with twins and ε-martensite produced during deformation. The work hardening rate was sustained from the continuous production of deformation products. The kinematic hardening contributed to the overall flow stress as a result of twins and ε-martensite acting as dislocation barriers. The mechanical behaviour of the alloy was modeled successfully by combining the yield strength, isotropic and kinematic hardening contributions to obtain the overall flow stress. Decohesion at γ – ε interfaces was observed to be the primary fracture mechanism. With the production of both twins and ε-martensite, the OAC alloy was labelled as a TWIP / TRlP steel.<br /> The Fe-22Mn-0.2C alloy had the lowest carbon content of the three alloys and contained an initial dual phase microstructure of austenite and ε-martensite plates. Straininduced ε-martensite was created during tensile deformation, with the kinematic hardening contribution resulting from the production of ε-martensite. An iso-work model was applied with contributions from the isotropic hardening of austenite and kinematic hardening of ε-martensite to the overall flow stress. Fracture was caused by separation along austenite - ε-martensite interfaces. The strain-induced ε-martensite created a TRlP effect within the O.2C alloy. <br /> Overall, the effect of carbon content on the microstructural evolution and mechanical properties within the Fe-22Mn-C system was determined. As the carbon content decreased, the SFE was lowered and a shift from the TWIP to TRlP effect was observed. The SFE phase map predictions were correct in predicting the as-annealed microstructure and deformation mechanism as determined by Allain et al. (Allain 2004b) and Nakano (Nakano 2010). The transformation kinetics and the role of carbon were not included in the SFE phase map predictions and were also factors to consider on the effect of carbon content on the Fe-22Mn-C alloys.</p> / Master of Applied Science (MASc)

<p>The unique combination of material properties has led to the extensive use of Sn 111 a wide range of industrial applications, making it one of the most important commercial materials. In this research work, an atomic scale computational model has been developed for Sn using Molecular Dynamics (MD). The MD simulation technique has proven to be quite effective in establishing quantitative models for different materials. But accurately modeling Sn using classical interatomic potentials in MD is quite difficult due to its complex crystal structure and phase stability. The Modified Embedded Atom Method (MEAM) has been used in this study as it includes angular forces present in materials with directional bonding, which can model both the metallic and covalent phase of Sn. Using this method, a previously published pure Sn potential has been modified to improve upon the melting properties. Some predictions are presented for thermodynamic quantities, phase stability, structural properties and elastic constants. Good agreement has been found with experiments for the melting point, the phase transition temperature and the latent heats; however the predicted elastic constants are somewhat greater than those found in the literature. The crystal - melt interface and its properties are also investigated with the new potential. The (001)[100] orientation of the interface is found to be atomically rough. Capillary Fluctuation Method (CFM) is used to compute the crystal - melt interface stiffness in this orientation and the interface kinetics is investigated with CFM and Free Solidification (FS) technique. The (100)[010] and (110)[1Ī0] oriented interface is found to be flat or atomically smooth. Wulff plot is constructed to determine the equilibrium shape of a single Sn crystal and an approximate measurement of the interfacial energy for the flat interfaces is presented.</p> / Master of Applied Science (MASc)

<p>Through the study of recovery, precipitation and their effects on recrystallization at various annealing temperatures, a physically based model was developed to describe recrystallization kinetics of Mg AZ31. Based on Zener drag calculations, precipitates in AZ31 had little effect on recrystallization. Recovery activation energy and activation volume were determined from yield stress vs. time experiments. Recovery kinetics were used to determine the stored energy remaining within the material throughout the annealing process. Recrystallization experiments showed that contraction twins were preferred regions of recrystallization and in-situ recrystallization experiments showed that twin/twin and twin/GB intersections were ideal locations for nuclei growth outside of the twinned volume. Given the deformation and the annealing temperature, the proposed model is able to predict the recrystallized fraction as a function of time. Future versions of the model may be used to construct recrystallization-time-temperature (RTT) maps as well as predict recrystallized grain size after a time of anneal. The model predictions are in excellent qualitative agreement with experimental observations and can capture nucleation growth within both the twins and matrix.</p> / Master of Science (MSc)

<p>The sputtering of high velocity particles is investigated through analysis by secondary photon emission. During a sputtering event a fraction of the particles emitted from the target are in varying degrees of excitation. These excited states have a finite probability of radiatively decaying back to the ground state. The emitted photon wavelength and intensity is recorded. In addition, the monochromator can be locked onto one particular wavelength and its intensity observed as a function of distance from the target surface. Such intensity distributions are measured for several group IA and IIA metals and fluorides. Their spatial extent, for the most part, is shown to be governed by the atomic transition probability of the excited state under observation.</p> <p>A model is developed to describe the intensity distribution based on the premise that the sputtered particles are distributed in energy and we further propose that excitation in a sputtering event is a threshold process. From the experimental intensity distributions this proposed threshold energy is deduced and is found to be 10¹ - 10³ eV. These relatively high kinetic energies, along with the large sizes of excited states, indicate that their creation involves large energy transfers at or very near the surface. Such events as recoil sputtering may lead to the production of excited states.</p> <p>To this end, calculations on recoil sputtering yields and mean energies are reported which justify the observed high energies and low yields. Further, a comparison, based upon fractional yields, of recoil sputtered atoms and high energy cascade sputtered atoms show that the recoil source provides a larger number of high energy atoms available for excitation. Results relating to recoil implantation yields are also presented. In addition, recoil phenomena is used to explain some preferential effects observed in sputtering and transient effects in secondary photon emission.</p> <p>Finally, the fate of the implanted primary ion is discussed with emphasis on its diffusion behavior in both damaged and undamaged ambient surroundings.</p> / Doctor of Philosophy (PhD)

<p>Using a newly developed method of co-electrodeposition, superparamagnetic films containing iron oxide nano-particles in a polymer matrix have been fabricationed. The method is based upon the electro synthesis of inorganic particles dispersed within a polymer matrix obtained by electrophoretic deposition. The results showed the prepared materials to exhibit superparmagnetic properties at room temperature. The influence of the deposition conditions and the electrolyte composition on the magnetic properties of the film have been studied. Adjusting the polymer content within the electrolyte has been shown to control the iron oxide to polymer composition ratio in the deposited film. This significantly affects the particle size, inter-particle distance and magnetic properties of the material. TGA analysis was used to determine the iron oxide to polymer composition ratio. The morphology of the films was studied by SEM and AFM techniques. Two theoretical approaches have been used to calculate the particle size in the developed films and the results are in good agreement with TEM observations. Saturation magnetization ranged up to 19.71 emu/g at room temperature in the films obtained. The blocking temperatures have been determined from the results of DC and AC measurements, the latter performed from 10 to 10,000 Hz. Blocking temperatures varied with film composition but remained below 111ºK. These results set the framework for discussion of the structure and magnetic properties of nano-materials synthesized using this fabrication method.</p> / Master of Applied Science (MASc)