Die-attachment, as the first level of electronics packaging, plays a key role for the overall performance of the power electronics packages. Nanosilver sintering has becoming an emerging solder-free, environmental friendly die-attach technology. Researchers have demonstrated the feasibility of die-attachment on silver (Ag) or gold (Au) surfaces by pressure-less or low-pressure (< 5 MPa) nanosilver sintering. This study extended the application of nanosilver sintering die-attach technique to copper (Cu) surface. The main challenge of nanosilver sintering on Cu is the formation of thick Cu oxide during processing, which may lead to weak joints. In this study, different processes were developed based on the die size: for small-area dice (< 5 * 5 mm2), different sintering atmospheres (e.g. forming gas) were applied to protect Cu surface from oxidation; for large-area dice (> 5 * 5 mm2), a double-print, low-pressure (< 5 MPa) assisted sintering process was developed. For both processes, die-shear tests demonstrated die-shear strength can reach 40 MPa. The effects of different sintering parameters of the processing were analyzed by different material characterization techniques. With forming gas as sintering atmosphere, not only Cu surface was protected from oxidation, but also the organics in the paste were degraded with nanosilver particles as catalyst. External pressure applied in the processing not only increased the density of sintered Ag, but also enhanced the contact area of sintered-Ag/Cu interface. Microstructure of Ag/Cu interface were characterized by transmission electron microscopy (TEM). Characterization results indicate that Ag/Cu metallic bonds formed at the interface, which verified the high die-shear strength of the die-attachment. Thermal performance of nanosilver sintered die-attachment on Cu was evaluated. A system was designed and constructed for measuring both transient thermal impedance (Zth) and steady-state thermal resistance (Rth) of insulated gate bipolar transistor (IGBT) packages. The coefficient of variation (CV) of Zth measurement by the system was lower than 0.5%. Lead-free solder (SAC305) was applied in comparison of thermal performance with nanosilver paste. With same sample geometry and heating power level, nanosilver sintered joints on Cu showed in average 12.6% lower Zth and 20.1% lower Rth than SAC305 soldered joints. Great thermal performances of nanosilver sintering die-attachment on Cu were mainly due to the low thermal resistivity of sintered-Ag and the good bonding quality. Both passive temperature cycling and active power cycling tests were conducted to evaluate the reliability of nanosilver sintered joints on Cu. For passive temperature cycling tests (-40 - 125 C), the die-shear strengths of mechanical samples had no significant drop over 1000 cycles, and nanosilver sintered IGBT on Cu packages showed almost no change on Zth after 800 cycles. For active power cycling test (Tj = 45 - 175 C), nanosilver sintered IGBT on Cu assembly had a lifetime over 48,000 cycles. The failure point of the assembly was the detachment of the wirebonds. Great reliability performances of nanosilver sintered die-attachment on Cu were mainly due to the low mismatch of coefficient of thermal expansion (CTE) between sintered-Ag and Cu. Meanwhile, low inter-diffusion rate between Ag and Cu prevented the interface from the reliability issue related to Kirkendall voids, which often took place in tin (Sn) -based solder joints. / Ph. D.

Roll press briquetting of coal-biomass mixtures presents a significant opportunity to address feedstock challenges associated with co-utilization of coal and biomass in existing coal-fired facilities. However, several technical and economic barriers require further investigation prior to industrial utilization of coal-biomass briquettes. The scientific contributions presented in this dissertation are intended to address the most critical technical challenges pertaining to coal-biomass briquette feedstocks. As with any product of an agglomeration process, the primary technical challenge regarding coal-biomass briquettes is achieving and maintaining a high level of quality from production to utilization. Several laboratory-scale research investigations were conducted to address this challenge. The first study was conducted to identify, develop and refine methods to characterize the most important physical properties indicative of coal-biomass briquette quality. The outcome of this work is a set of recommendations for novel and refined methods to characterize important coal-biomass briquette properties. The second study was conducted to develop a novel method to identify the optimum water content of coal-biomass blends prior to briquette production. As a result of this study, the Briquette Proctor Test was developed to minimize the time and materials required to identify the optimum water content that corresponds to maximum quality of coal-biomass briquettes. The third study was conducted to evaluate the influence of feedstock variables, additive variables, and roll press operating parameters in the production of coal-biomass briquettes from various coal and biomass types. From this study, the influence of each parameter on the quality of briquettes was determined and optimum conditions were identified for a variety of coal-biomass mixtures. The fourth and final study was conducted to develop and evaluate methods to improve the water resistance of coal-biomass briquettes using wood-derived chemicals. Using these chemicals, the novel coating method developed in this study significantly improved the water resistance and weathered durability of coal-biomass briquettes. / Ph. D.

Three phases of work were performed for this study. First a new form of liberation analysis was created and applied to two coal samples from separate formations. This new method of liberation analysis attempts to remove sources of error found in the traditional form of liberation analysis. This new method is capable of producing results comparable to multiple iterations of the traditional liberation analysis while using only one head sample. The new method relies on the mathematical reconstruction of the data to produce the resulting liberation profile. This allows the user to easily expand the method to include more liberation profiles without greatly increasing the amount of head weight needed. The results of this phase confirm that the products of each liberation profile reconstitute the correct feed ash. The second phase of work focused on the evaluation and concentration of rare earth elements (REEs) present in the refuse streams of coal processing plants found in the eastern United States. Twenty plants were sampled for the fleet study. Samples of these plants' refuse streams were collected and their REE and ash contents were determined. Coal from the Eagle seam, Fire Clay seam, and Fire Clay Rider were collected and tested during the concentration phase. Samples of a waste coal from the Pittsburgh seam and a coal combustion by prodcut were also provided by a third party. The separation methods investigated include multi-gravity separation, electrostatic separation, and selective oil agglomeration. Partition curves from x-ray sorting devices were also applied to REE float-sink data as well. The results of this work show that REEs tend to partition with low ash material when viewing the results on an ash basis. Finally, the third phase of this work involved the application of x-ray sorting technology on different coals. This work showed that the x-ray sorting technology in question is capable of effectively treating prescreened feed with a size range of 2" x 1/4". The work also shows that the x-ray sorting technology also has applications in the power generation field, where it can be used to eliminate elements of environmental concern. / Ph. D.

No description available.

Microporous carbonates host a significant portion of the remaining oil-in-place in the giant carbonate reservoirs of the Middle East. Improved understanding of petrophysical and multi-phase flow properties at the pore-scale is essential for the development of better oil recovery processes. These properties strongly depend on the 3D geometry and connectivity of the pore space. In this study, we harnessed the unique capabilities of fluorescence confocal laser scanning microscopy (CLSM) to capture both macroporosity and microporosity, down to 0.1 µm, to provide a more representative 3D representation of pore space compared to traditional methods. The experimental procedure developed was specifically designed to enable highresolution confocal 3D imaging of the pore space of carbonate systems. The protocol aims to render carbonates more "transparent" to CLSM by imaging etched epoxy pore casts of the sample and minimizing CLSM signal scattering. The resulting highquality 3D images of the multi-scale pore space allow more reliable petrophysical interpretation and prediction of transport properties. Additionally, we present a robust pore imaging approach that correlates 2D images produced by scanning electron microscopy (SEM) with the 3D models produced by CLSM that cover a range of scales, from millimeters in 3D to micrometers in 2D. For the first time, multi-color fluorescence confocal imaging was employed to characterize the geometric attributes of a porous medium. We foresee that the protocol developed in this study could be used as a standard protocol for obtaining high-quality 3D images of epoxy pore casts using confocal microscopy, and could contribute to improved characterization of micritic carbonate reservoirs and oil recovery methods. We also demonstrate the advantages of multi-scale and multi-color confocal images in realizing more accurate evaluations of petrophysical properties. Finally, we demonstrate that micro 3D printing (two-photon polymerization) can potentially be used to fabricate micromodels with sufficient resolution to capture the geometric attributes of micritic carbonates and that can replicate the inherent 3D interconnectivity between macro- and micro-pores.

No description available.

Rechargeable lithium ion batteries are common materials in everyday applications. The most frequently used cathode material, LiCoO2, provides high energy density and stable charge/discharge performance. However, LiCoO2 is toxic and relatively expensive, therefore, other alternatives are being sought after in the development of battery materials, such as LiMn0.33Ni0.33Co0.33O2 (identified commonly as 333 compound). The 333 compound is now popular due to its comparable performance with LiCoO2, lower price, enhanced stability, and more environmentally friendly characteristics. In addition, Li1.2Mn0.54Ni0.13Co0.13O2 (HENMC) is still on the stage of testing and it attracts wide attention due to its higher rechargeable capacity and thermal stability. However, there are still challenges confronted: cycle stability and low rate capability. In order to verify all the roles played by different elements shown in NMC materials and explore the corresponding performance with different formula units, compositional analysis is needed. ICP-MS (inductively coupled plasma mass spectrometry) can provide bulk compositional information and has been used in recent work, giving a general idea of the composition of NMC materials. However, compositional inhomogeneity analysis has usually been neglected in these studies. Therefore, the objective of this work was to explore this variation in composition locally with higher spatial resolution, at the NMC particle level. This work was carried out through the use of scanning electron microscopy – energy dispersive spectroscopy (SEM-EDS) and Auger electron spectroscopy (AES). Furthermore, nano-scale quantitative analysis was done with transmission electron microscopy – energy dispersive spectroscopy (TEM-EDS). Moreover, an optimal approach and procedure of compositional analysis by using EDS and AES was explored with proper standards and operation conditions to provide consistent and stable results. The optimal quantification method was applied to investigate the compositions of 333 compound before and after ball milling and HENMC specimen before and after cycling. The results support the structural changes and in turn the electrochemical performance of the battery material. In the 333 compound, the electrochemical performance of the battery was deteriorated due to ball milling, during which Zr was introduced and particles were more compact. In HENMC, during cycling, the Mn distribution was homogeneous at the beginning, then inhomogeneous and homogeneous again, supporting the hypothesis of the transformation of phases: formation of spinel phase and potential SEI layer. In-depth structural analysis of different NMC materials has been reported previously by other groups. However, the structural effects due to cycling, within particles still needs investigation. Therefore, X-ray diffraction (XRD) was used to investigate the bulk material crystalline structure. Local nano-scale level structural variations amongst different isolated primary particles were investigated by the electron diffraction pattern based on TEM. The 333 compound and HENMC cycling was examined before and after cycling. After cycling, in the 333 compound, the O1 phase domains with P-3m1 space group appear inside the O3 phase with R-3m lattice. With more cycling, more domains appear. For HENMC, the original pristine samples exhibit the rhombohedral and monoclinic phases. After cycling, more and more spinel phase appear. Finally, after 100 cycles, we observe evidence of the potential solid electrolyte interphase (SEI) formation. In all, all the results above support the phase changes of 333 compound and HENMC. More investigations are needed to understand the degradation process of both compounds. / Thesis / Master of Materials Science and Engineering (MMatSE)

<p> Part One deals with thin films of SnO₂ which were prepared by ion-beam sputtering, reactive sputtering and anodic oxidation. The films were found to be either amorphous or crystalline in their prepared state. </p> <p> The structure of the as-deposited amorphous films, as revealed by transmission electron microscopy, presented interesting features: there was a continuous structure in the case of high-temperature deposition, whereas an "island structure" was revealed in the case of low-temperature deposition. Furthermore, heat treatment of films having an "island structure" showed this structure to be maintained provided the heating was done with unsupported films, while the structure became continuous when heat treatment was performed on supported specimens. </p> <p> The crystalline form of the films has been worked out, and found to generally be cassiterite; nevertheless a phase different from cassiterite has been occasionally noticed during this work. In some cases it could be tentatively identified as SnO, while other cases it remains unidentified. Crystallization temperatures found here are somewhat different from those indicated in the literature, namely: 500, 300, 225ºC according to substrate temperature and nature and type of heat treatment. Anodic oxidation of tin has been performed(apparently for the first time) in a non-solvent electrolyte, the films being consistently crystalline. </p> <p> The results obtained in the case of films deposited on water-cooled substrates, have revealed a dependence of film structure on film thickness and this effect has been confirmed in supplementary experiments. Thus thick films appear to crystallize spontaneously at room temperature. </p> <p> Part Two deals with radiation damage studies. Our experiments on krypton-ion bombarded SnO₂ films show that amorphous specimens remain amorphous following ion bombardment. The electron-microscope evidence of whether crystalline SnO₂ is amorphized by ion bombardment was tentatively negative, while the gas-release evidence was strongly negative. </p> Part Three deals with diffusion in inert-gas implanted SnO₂. In the first section we give the theoretical background that enabled us to deduce from our experiments rough estimates of the melting temperature, self-diffusion temperature. and activation-energy for self-diffusion of the less mobile ion in SnO₂. In particular, we obtain the following results: </p> <p> T_melting = 2600 - 3000ºK </p> <p> T_self-diffusion = 1480 - 1870ºK for a 2 min. time scale and 134±44Å distance scale. </p> <p> ∆H_self-diffusion = 87,200 - 131,00 cal/mole </p> <p> Note that the melting point for tine oxide is variously reported in different handbooks to lie between 1400 and 2200ºK. From a comparison with other work we have concluded that our value for ∆H is very likely that for oxygen-ion diffusion. </p> / Thesis / Master of Science (MSc)

Ochre is a culturally significant material that is commonly recovered from archaeological sites. However, despite its ubiquity it has yet to realize its full interpretive potential as an artifact of archaeological inquiry, specifically in the context of geochemical characterization studies. Studies of this type, often referred to as ‘sourcing’ studies, involve the application of techniques in radiation physics to determine the elemental composition of artifacts and raw materials. These data are then used interpret patterns of behaviour in the procurement, movement, and trade of different artifact classes such as obsidian, chert, or ceramic. By comparison, geochemical characterization studies centred on ochre-related activities are fewer in number. This thesis consists of three case studies that developed methodological foundations for the geochemical study of ochre in regions of British Columbia and Ontario, Canada, respectively. Using instrumental neutron activation analysis and X-ray fluorescence, ochre from geologic outcrops and archaeological sites were analysed to determine their elemental composition. Multivariate statistical tests, including principal components and canonical discriminant analyses, were conducted to explore patterns and variability in ochre geochemistries. The results described in the following papers demonstrate the challenges and limitations for characterization studies of ochre, and present considerations for expanded research in these geographic regions. This thesis offers contributions to broader topics of discussion in archaeological sciences, such as the accurate and precise acquisition of geochemical data, the role of geologic scales and diagenetic processes on the chemistries of iron oxides, how to identify and interpret patterns in elemental data sets, and the utility and limitations of portable analytical technologies. This research has established important methodological foundations for the study of ochre in British Columbia and Ontario, and has demonstrated the potential for expanded analysis of materials from additional archaeological sites and geologic outcrops. This will enable the future interpretation and regional synthesis of patterns and networks of ochre-related activities, including quarrying and procurement, trade and exchange, and variability in use contexts. / Dissertation / Doctor of Philosophy (PhD)

<p> Biodegradation of benzene, a common groundwater contaminant, occurs readily in the presence of oxygen; however, at contaminated sites, aerobic bacteria often deplete the available oxygen, resulting in anaerobic conditions. Field and laboratory studies have shown that the anaerobic biodegradation of other aromatic hydrocarbons such as toluene occurs readily, while anaerobic benzene biodegradation has only been documented in a handful of studies. Despite these difficulties, benzene biodegradation has been shown to occur under iron-reducing, sulphate-reducing and methanogenic conditions, but not under nitrate-reducing conditions.</p> <p> The goal of this thesis research was to enrich and characterize the benzene-degrading microbial populations in microcosms and transfer cultures derived from soil from four different sites. Cultures were amended with potential exogenous electron acceptors (nitrate, sulphate, ferric iron) and the rates of biodegradation under different terminal electron accepting processes were determined. Sustained, anaerobic benzene biodegradation was obtained in transfer cultures containing less than 1% of the original soil inoculum. The rate of benzene degradation was variable, ranging from 1 μM/d to more than 75 μM/d. Growth of bacteria was linked to benzene degradation under sulphate-reducing and nitrate-reducing conditions. Growth was very slow, with doubling times of 9-30 days estimated by modelling benzene depletion curves to the Monod kinetic equation. The rate of benzene degradation was influenced most by biomass concentration and much less by the terminal electron accepting process.</p> <p> The ratio of moles of electron acceptor depleted to moles of benzene degraded was calculated and compared to the theoretically predicted ratios to confirm putative terminal electron acceptors. Anaerobic benzene degradation linked to iron reduction, sulphate reduction and methanogenesis was observed in enrichment cultures, corroborating results from previous studies. In addition, in some enrichment cultures, benzene degradation was linked to nitrate reduction. This is the first report demonstrating benzene degradation linked to nitrate reduction.</p> / Thesis / Master of Engineering (MEngr)