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<p>A study was undertaken to achieve a better understanding of the key microstructure-performance relationships involved with the intergranular corrosion and exfoliation corrosion of Cu-lean AA7003 alloy extrusions, as a function of the heat-treated condition. The heat treatments of interest in this study include the naturally-aged T4 condition, representing the as-extruded condition, an artificially-aged T6 condition, representing a post-weld stress-relief condition, and an artificially-aged automotive paint-bake cycle condition. The influence of heat treatment on the resultant microstructure is characterized using light optical microscopy, coupled with image analysis, and electron (scanning & transmission) microscopy, coupled with energy dispersive spectroscopy. The influence of heat treatment on the corrosion behaviour is characterized using anodic polarization measurements and ASTM standardized testing to evaluate the susceptibility resistance to intergranular corrosion (ASTM G110) and exfoliation corrosion (ASTM G34).</p> <p>The cross-sectional (LT-ST & L-ST) microstructures of all three heat treatments consist of a fibrous, non-recrystallized grain structure in the interior, and a coarse recrystallized grain structure at the exterior surface. Both grain structures are slightly elongated along L-direction. The grain size distribution and grain aspect ratio distribution is weakly dependant on the heat treatment applied, and on the orientation plane. Among the two artificial aging, the T6 (post-weld stress-relief) condition has the higher micro-hardness (yield strength), as it has higher density (volume fraction) of the strengthening MgZn₂-type precipitates (η, η′ and their GP zones) within the Al matrix grains.</p> <p>Anodic polarization measurements show a more negative corrosion potential (E_corr) for the two artificially aging heat-treated conditions. The shift is believed to be due to the micro-galvanic cell activity established between the more noble Al matrix grains and the more active strengthening MgZn₂-type precipitates within the Al matrix grains, which have a significantly increased surface area (volume fraction) in the artificially-aged condition. A similar, single breakdown potential (E_b) corresponding to a pitting potential (E_pit) is observed, regardless of the heat-treated condition. The similar potential is believed to be due to localized breakdown of the passive film at the periphery of coarse second phase intermetallic particles (Al₃Fe), which remain unaffected by artificial aging.</p> <p>Of the three heat-treated conditions studied, the T6 condition exhibits the lowest susceptibility to both intergranular corrosion and exfoliation corrosion. The lower susceptibility is believed to be due to the lack of any Cu enrichment in across the grain boundary region (either in the solute depted zone or in the generic Mg(Zn,CuAl)₂ grain boundary precipitates). This lack of enrichment is believed to produce a smaller micro-galvanic cell activity across the grain boundary region, as compared to that produced when Cu is enriched across the grain boundary region, particularly in the Solute depted zone (SDZ).</p> <p><br /></p> / Master of Applied Science (MASc)

Due to the rising health care costs and with the advent of biogenerics, there is a growing demand to develop new and reliable techniques to characterize proteins and biopharmaceuticals. In addition, characterization aids in understanding the intricate relationship between a protein's structure and its function. To address this challenge, two protein structural parameters, 1) amino acid surface area and 2) amino acid microstructure, were chosen to be investigated. Two chromatographic techniques, 1) ion exchange chromatography (IEC) and 2) immobilized metal affinity chromatography (IMAC), were used to characterize the above-mentioned protein structure parameters. The model protein chosen for our work is T4 lysozyme. The protein consists of 164 amino acids with molecular weight ~ 18 kD. SYBYL 7.1 software was used to generate in silico point mutants. Two categories of protein variants (point mutants) were generated using site-directed protein mutagenesis. The goal for generating point mutants was to obtain mutants that vary in the two structural parameters. The first category point mutants vary in the surface accessibility of a surface accessible histidine residue. The second category point mutants predominantly vary in protein net charge and the amino acid microstructure. In total, seventeen point mutants were generated: 1) category I consists of seven variants that vary predominantly in their histidine surface accessibility, and were obtained by replacing a charged amino acid residue at different locations on the surface of the protein molecule, and 2) category II consists of ten variants that vary in both net charge and charge distribution were obtained by replacing charged and neutral amino acid residues at different locations (different microenvironments) on the protein surface. PCR technique was used to generate the point mutants. Gene and protein sequencing were employed to confirm the veracity of point mutation. CD and Lysozyme activity assays were performed to determine whether or not the 3D structure of all the protein variants was intact. Zonal analysis was used to obtain the binding strength values of all seventeen variants in IMAC with copper as the immobilized metal ions, and gradient elution method was used to obtain the relative retention times (rRT) values of all the variants in IEC. The seven lysozyme variants generated in category I each contains one surface histidine residue. In IMAC, there is a correlation between the surface accessibility of the lone surface histidine and the protein's binding strength with R²⁺= 0.76. In IEC, the correlation between the protein's microstructure, which predominantly consists the surface accessibility of the histidine residue, and the protein's retention times was R²⁺= 0.95. However, there were few outlier variants (e.g. variant K83H) which did not follow the correlations. The variations presented by few outlier variants can be attributed to the presence of intramolecular bonds, which restrict the mobility of the amino acid side chains and subsequently hinder the specific interaction between the amino acid residue and chromatographic media. For category II variants, short and medium range charge perturbations around the sole histidine residue in T4 lysozyme were engineered within 15 Ã distance of histidine. There was a strong correlation (R²⁺ = 0.96) between the theoretical (DeltaDeltaGElec) values, calculated using simple Coulomb's law, and the experimental (DeltaDeltaGB) values, which were obtained by measuring the protein binding strength values using IMAC. Similar correlation (R²⁺= 0.93) was obtained between the change in net charge (-2 to +2 units) and the relative retention times in IEC. Similarly, there were few variants (e.g. S136K, R76D) that did not follow the trends. The deviations of the few outlier variants can be attributed to the presence of unique microstructure effects around the histidine residue. These microstructure effects were quantified in IMAC as (DeltaDeltaGMicro), and in IEC they were quantified by the change in rRT values. In summary, all seventeen variants had different binding strengths and rRT values indicating the variation in the protein structure around the histidine residue. Our work reveals that it is possible to capture the microstructural effects of a protein through the combination of protein molecular modeling and simple chromatographic experiments. / Ph. D.

The major goal of the work is to develop effective additives for U-10Zr (wt.%) metallic fuel to mitigate the fuel-cladding chemical interactions (FCCIs) due to fission product lanthanides and to optimize the fuel phase mainly by lowering the gamma-onset temperature. The additives Sb, Mo, Nb, and Ti have been investigated. Metallic fuels with one or two of the additives and with or without lanthanide fission products were fabricated. In this study, Ce was selected as the representative lanthanide fission product. A series of tests and characterizations were carried out on the additive-bearing fuels, including annealing, diffusion coupling, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and differential scanning calorimetry (DSC). Sb was investigated to mitigate FCCIs because available studies show its potential as a lanthanide immobilizer. This work extends the knowledge of Sb in U-10Zr, including its effect in the Zr-free region. Sb forms precipitates with fuel constituents, either U or Zr. However, it combines with the lanthanide fission product Ce when Ce is present. Those Sb-precipitates are found to be stable upon annealing, and are compatible with the cladding. The additive does not change the phase transition of U-10Zr. Mo, Nb, and Ti have been investigated for phase optimization based on the known characteristics shown in the binary phase diagrams. The quaternary alloys, i.e., two Mo-bearing alloys and two Nb-bearing alloys, were investigated. Compared to U-10Zr, a few weight percentages of Zr are replaced by those additives in the quarternary alloys. The solid-state phase transitions were determined (alpha and U2Ti transfer into gamma). The transition temperature varies depending on the compositions. The Mo-bearing alloys have lower -onset temperatures than the Nb-bearing alloys. All of them have lower gamma-onset temperatures than that of U-10Zr. Since low gamma-onset temperature is favorable, the results indicate that the fuel phase can be optimized by the replacement of a few weight percentages of Zr into those additives. All the experiments were out-of-pile tests. Therefore, in-pile experiments will be necessary to fully evaluate the performance of the additives in the future. / Doctor of Philosophy / Fuel is the "heart" of a nuclear reactor, and fuel development is a key to improving the performance and reliability of a nuclear reactor. This study investigated the effects of metallic fuel additives in a sodium-cooled fast reactor (SFR). SFRs are an advanced reactor design. Metallic fuel, e.g., U-10Zr (wt.%), is one of the common candidates for SFR fuel. The aim of this study is to develop effective additives for U-10Zr metallic fuel to improve fuel performance. The study has two main objectives. The first one is to mitigate the fuel-cladding chemical interactions (FCCIs), while the second one is to optimize the fuel phase. Four additives, i.e., Sb, Mo, Nb, and Ti have been investigated. The study is a pioneer for the application, thus, the experiments were performed without considering the irradiation effect. Metallic fuels with one or two additives were fabricated, with a series of tests being performed at a laboratory scale. The additive, Sb, was used to mitigate the FCCIs, since FCCIs are a limitation of fuel utilization (i.e., burnup). Lanthanides are produced during fuel operation and attack cladding, being one of the reasons for FCCIs. It is known that the additive Sb has the potential to bind lanthanides into stable precipitates. This work brings the investigation a step further, providing more evidence to demonstrate the stability of the precipitates and the compatibility with cladding. The results are favorable as they demonstrate that the lanthanides will not attack the cladding if they can be caught by the additive Sb in the fuel. The additives Mo, Nb, and Ti were investigated to optimize the phase. One of the favorable phase properties is the gamma-onset temperature - the lower the better. For example, the gamma-onset temperature is 776°C in pure U, while it is 680°C in U-10Zr (meaning that 10 wt.% Zr lowers the gamma-onset temperature by 96°C). In this work, the exploration moves forward by replacing a few percentages of Zr with Mo+Ti, or Nb+Ti. After the change, the gamma-onset temperatures are further decreased, with the temperatures decreasing more in the Mo-bearing fuels than in the Nb-bearing fuels. The significance of this work is twofold. Firstly, it extends the knowledge of Sb as an additive for mitigating FCCIs; secondly, it shows that Mo, Nb, and Ti can optimize the fuel to achieve a favorable phase property. The results provide strong reasons for additional irradiation tests in the future.

Porous silica-based nanocomposites are promising ceramics, as they exhibit high specific surface area, highly porous network, and a surface that can be easily functionalized. This dissertation describes the results of a study on the formation and properties of porous silica nanoparticle-based composites, using techniques of freeze casting and sintering. Kaolinite platelets and silica nanorods were added into the nanoparticle system, and their effects on modifying the porous microstructures and physical properties were investigated. During freeze casting, homogeneous microstructures with highly interconnected porosity are fabricated. Kaolinite addition results in large and more interconnected pores, while added silica nanorods cause a pore morphology evolution from circular to elongated spherical pores with increasing aspect ratio. The specific surface areas (area/mass) of the particles are conserved during freeze casting and values for the resulting composites can be accurately predicted using the area and mass of the components assuming conservation of area. Both kaolinite platelets and silica nanorods effectively improved the strength of the freeze cast green composites as they distribute any applied stress over a larger portion of the sample. Upon sintering, added kaolinite is found to modify the sintering behavior of the silica nanoparticles and a transitioning interfacial phase is identified when sintering temperature is above 1250 °C. This new phase contributes to the further enhancement of strength and this strengthening effect depends on composition and initial solids loading. After sintering at 1250 °C for 1 h, a ceramic containing 10 vol% kaolinite and 8 vol% silica has a maximum strength while maintaining a ~69% porosity. The kaolinite-silica composites with lower solids loading exhibit faster sintering (e.g. larger shrinkage, more extensive thickening of the pore walls), which, in turn, results in a rapid increase in mechanical strength. Based on the understanding of the composite properties and the underlying principles, a novel method for creating nanocomposites with precisely controllable specific surface area is developed. With repeated nanoparticle suspension infiltration, freeze drying, and sintering, the specific surface area can be varied from less than one to well over 100 m2/g, demonstrating potential application as liquid membranes. / Ph. D.

As advances in solid rocket technology push rocket motors to more extreme operating speeds and temperatures, it becomes increasingly important to have well-designed material systems capable of surviving these harsh conditions. One common component in these systems is the use of a fiber- and particle-reinforced EPDM insulation layer between the motor casing and the solid fuel to shield the casing from the temperatures of the burning fuel and from the high velocity of gas particles traveling within the motor. This work studies several insulation materials to determine which exhibits the highest shear strength after being charred. Double-notch shear test specimens of three materials, ARI-2718, ARI-2719, and ARI-2750, were charred and tested to measure the failure strength of each charred material. The ARI-2750 showed the highest shear strength when loaded along the material orientation, but the ARI-2719 was strongest when transversely loaded. The strength measurements for ARI-2750 were highly sensitive to loading direction, unlike ARI-2718 and ARI-2719. Extensive scanning electron microscopy to identify correlations between shear strength and microstructure revealed that the amount of fiber orientation and amount of residual matrix material may have significant impacts on charred shear strength in these materials. / Master of Science

Yes / This paper investigates the influence that information asymmetry may possess upon the future volatility, liquidity, market toxicity and returns within cryptocurrency markets. We use the adverse selection component of the effective spread as a proxy for overall information asymmetry. Using order and trade data from the Bitfinex Exchange, we first document statistically significant adverse selection costs for major cryptocurrencies. Our results also suggest that adverse selection costs, on average, correspond to ten percent of the estimated effective spread, indicating an economically significant impact of adverse selection risk on transaction costs in cryptocurrency markets. We finally document that adverse selection costs are important predictors of intraday volatility, liquidity, market toxicity, and returns. / Türkiye Bilimler Akademisi. Grant Number: Outstanding Young Scientist. / The full-text of this article will be released for public view at the end of the publisher embargo on 11 Jan 2025.

Yes / Diffusion brazing of SiC ceramic to IN738 using an Ag-Cu-Ti powder-mixture as an interlayer was carried out for the first time. The impact of the bonding time (30 and 45 min) on metallurgical features and shear strength of the joints was assessed. The results revealed that raising the bonding time resulted in expanding of the brazing layer from 46.98 µm to 55.31 µm. Besides, increasing the bonding time also enhanced the shear strength of the SiC/Ag-Cu-Ti/IN738 joints.