Recent Submissions

  • Approach to beneficiation of spent lithium-ion batteries for recovery of materials, An

    Mishra, Brajendra; Marinos, Danai; Anderson, Corby G.; Spiller, D. Erik (Colorado School of Mines. Arthur Lakes Library, 2014)
    Lithium ion batteries are one of the most commonly used batteries. A large amount of these have been used over the past 25 years and the use is expected to rise more due to their use in automotive batteries. Lithium ion batteries cannot be disposed into landfill due to safety reasons and cost. Thus, over the last years, there has been a lot of effort to find ways to recycle lithium ion batteries. A lot of valuable materials are present in a lithium ion battery making their recycling favorable. Many attempts, including pyrometallurgical and hydrometallurgical methods, have been researched and some of them are already used by the industry. However, further improvements are needed to the already existing processes, to win more valuable materials, use less energy and be more environmentally benign. The goal of this thesis is to find a low-temperature, low-energy method of recovering lithium from the electrolyte and to develop pathways for complete recycling of the battery. The research consists of the following parts: Pure LiPF6 powder, which is the electrolyte material, was characterized using x-ray diffraction analysis and DSC/TGA analysis. The LiPF6 powder was titrated using acid (HCl, HNO3, H2SO4), bases (NH4OH) and distilled water. It was concluded that distilled water was the best solvent to selectively leach lithium from lithium-ion batteries. Leaching conditions were optimized including time, temperature, solid/liquid ratio and stirring velocity. All the samples were tested using ICP for chemical composition. Because leaching could be performed at room temperature, leaching was conducted in a flotation machine that was able to separate plastics by creating bubbles with no excess reagents use. The solution that contained lithium had to be concentrated more in order for lithium to be able to precipitate and it was shown that the solution could be concentrated by using the same solution over and over again. The next set of experiments was composed of battery shredding, steel separation by hand magnet, leaching with distilled water and sizing using wet sieving. Every fraction was sent to rare-earth rolls separation and eddy current separation. A size distribution analysis was conducted and the fractions were analyzed using ICP .
  • Aspects of time-lapse electrical resistivity monitoring in geotechnical and reservoir problems

    Li, Yaoguo; Putman, Brent D.; Batzle, Michael L.; Hale, Dave, 1955-; Nabighian, Misac N. (Colorado School of Mines. Arthur Lakes Library, 2014)
    Internal erosion can be present in almost any environment in which fluid flows through a rock matrix. In almost all cases this phenomenon is a problem to be avoided. Internal erosion weakens the rock structure, which can cause collapse of the surrounding matrix. In the geotechnical field, this is most common with earthen dams and levees. The consequence of internal erosion in an oil and gas reservoir setting is to create a high-permeability link between injection and production wells, by-passing resource containing volumes of the reservoir. In this thesis, I present feasibility studies to examine the effectiveness of electrical resistivity tomography (ERT) for monitoring both fluid flow and the resultant internal erosion. This is conducted in both the laboratory and reservoir scales. Because the success of ERT is highly dependent on the configuration of electrodes, significant time is spent on developing configurations that image internal erosion while also limiting the number of data required. This work gives evidence that ERT can have beneficial use in the geotechnical monitoring scenario. The feasibility study for the small-scale geotechnical experiment on internal erosion shows that a 10 cm diameter sample can be imaged effectively when the electrode configuration is properly designed. This feasibility study is further confirmed through a data set collected in the laboratory. This experiment produced sufficient results in terms of the model recovered through inversion. The feasibility study evaluating ERT in a reservoir setting shows that the monitoring target is the total 410 m long swept zone, rather than the small fractures, due to low signal strength from the fractures. The capability of ERT in the reservoir scenario depends on the degree of internal erosion and the electrode configuration used to take measurements. If data can be collected in boreholes in close proximity to the swept zone, then ERT has a potential beneficial application in monitoring fluid flow and associated fractures.
  • Structural geology and geochemistry of sedimentary rock-hosted gold in the eastern Nadaleen Trend, Yukon Territory, Canada

    Kuiper, Yvette; Palmer, Justin C.; Monecke, Thomas; Hitzman, Murray Walter; Emsbo, Poul (Colorado School of Mines. Arthur Lakes Library, 2014)
    Recently discovered gold (Au) in the eastern Nadaleen Trend of northeastern Yukon Territory is hosted in unmetamorphosed Neoproterozoic carbonate and siliciclastic rocks that were subject to intense deformation prior to Au mineralization. Intense deformation in the region resulted from mid-Cretaceous NNE-vergent, thin-skinned fold-thrust deformation. Structures within a 6 km2 area at the eastern Nadaleen Trend are complex and are not recognized elsewhere in northeastern Yukon Territory. Field observations suggest these rocks are the product of NNE-SSW-directed shortening (D1), NW-SE-oriented dextral simple shear (D2), and N-S-directed shortening (D3) followed later by minor dextral slip (D4). The complicated geometry of the area may result from the presence of basement structures and/or competency contrasts between rock units within the sedimentary package. The eastern Nadaleen Trend lies within an E-trending triangle zone bounded by S- and N-vergent reverse faults to the north and south, respectively. The triangle zone does not continue to the west or east. To the west, rocks consist of multiple NNE-verging structures in the south and only one map-scale fold in the north indicating that strain decreases northwards. Rocks in the east are consistently NNE-vergent. This change in structural style suggests that NNE-directed transport in the rocks to the west was obstructed at the latitude of the eastern Nadaleen Trend while transport in the east was unobstructed. Potential causes for the obstruction include rheological heterogeneity or a subsurface structure. The obstruction is nearly co-spatial with the steep southward transition from both Neoproterozoic and Paleozoic platform rocks to basin rocks. This abrupt platform-to-basin transition occurred in this location throughout much of geologic history, suggesting that the location of the transition may be pinned by a pre-existing basement feature. For this reason, we suggest that mid-Cretaceous deformation patterns were influenced by a subsurface basement fault that obstructed NNE-directed fold-thrust movement to the west of the eastern Nadaleen Trend. The structure's interpreted eastern edge below the eastern Nadaleen Trend may have presented a minor obstruction that resulted in the formation of a triangle zone. East of the eastern Nadaleen Trend, fold-thrust related movement was unobstructed. Between unobstructed rocks in the east and obstructed rocks in the west, a strike-slip interface is interpreted to occur that may have influenced the orientation of oblique folds that occur within the eastern Nadaleen Trend. Major Au deposits within the eastern Nadaleen Trend occur within moderately to steeply S- to SSW-plunging anticlines and not within folds in other orientations or synclines. The orientation of the folds that host Au is oblique to the regional trend and they occur within the E-trending triangle zone. Reverse faults bounding the triangle zone are interpreted to have acted as an aquitard below which ore fluid migrated updip. Within the eastern Nadaleen Trend, ore fluid migration was concentrated into hinge zones of SSW-plunging anticlines, which may have acted as local fluid conduits. One of the Au zones, the Conrad zone, is situated in the northeast part of the eastern Nadaleen Trend and within a steeply SSW-plunging anticline that folds fine-grained siliciclastic rocks overlying silty limestone. This anticline is cutoff to the north by a ~50 m wide NNE-dipping fault zone. Deep within the Conrad zone, Au dominantly occurs within the anticline hinge zone, suggesting that ore fluid indeed may have risen along the fold hinge zone. Relatively more Au occurs at shallower levels, perhaps because the (now eroded) juxtaposed anticlinal fine-grained siliciclastic rocks and fault zone presented a natural trap that slowed upward fluid migration. If fluid upwelling was restrained in this zone, it could have prolonged the interaction time between ore fluid and the host rock that may have led to increased Au deposition. Fluid-rock interaction within the Conrad Au zone changed equilibrium conditions in both the ore fluid and the host rock. The change in conditions destabilized certain components of both the host rock and the ore fluid that resulted in an elemental flux between the two. This flux is preserved within the host rock where certain elements show enrichments or depletions in the presence of Au. Within the Conrad zone, Ca, Mg, and Na are depleted in Au-bearing samples suggesting that the fluid that brought in Au also facilitated a loss of carbonate minerals. Elements enriched in Au-bearing samples include S, Au, As, Sb, Hg, Tl, Te, Cu, Pb, Zn, Bi, Ni, Fe, Ba, Li, and Cd suggesting that they were brought in with the ore fluid. Au-bearing samples have an S/Fe value near 1.15, suggesting an association exists between Au and pyrite (FeS2; 46.7 wt. % Fe). The geochemical features above show strong geochemical similarities to Carlin-type deposits in Nevada, USA.
  • Metabolic and physiological engineering of photosynthetic microorganisms for the synthesis of bioenergy feedstocks: development, characterization, and optimization

    Posewitz, Matthew C.; Spear, John R.; Work, Victoria H.; Munakata Marr, Junko; Cohen, Ronald C.; Dean, Anthony M. (Colorado School of Mines. Arthur Lakes Library, 2014)
    Biological processes are the reason for Earth's hydrocarbon reservoirs and its oxygenated atmosphere. Life would be different today if not for the advent of photosynthetic carbon reduction by cyanobacteria 3 billion years ago. Oxygenic photoautotrophy uses carbon dioxide (CO2) from the air, the radiant energy of sunlight, and reductive potential abstracted from water to derive structural carbon. The simplicity of this concept is rivaled by the complexity of its constituent mechanisms, but this has not inhibited the vast diversity of plantlife throughout the ages. Photosynthetic organisms thrive in most photic environments in unicellular and multicellular forms. It is testament to evolution that anthropologic efforts now seek to understand these life forms for their biosynthetic, photophysiological, and adaptive properties. Of particular interest is the possibility to direct the metabolism of CO2-reducing organisms into bioproducts of practical significance in modern human lifestyle. One perception is that combustible molecules could be synthesized by these organisms, recovered for conversion to a fuel source, and once utilized as such, the products (CO2 and water) could be reconverted into the same reduced carbon compounds by the same organisms. Taking the model of carbon neutrality to its fruition is as sensitive, multifaceted, and profoundly complex an endeavor as bringing the concept of photosynthesis into reality. The characterization of photosynthetic microorganisms (PSMs) has been widely pursued for over 50 years, and the study of photosynthesis even longer. Still requiring much clarity, research has begun to manipulate photosynthetic metabolism for desired effects. This thesis defines the physiologies of two distinct classes of PSMs, green algae and cyanobacteria, under conditions to assess the strains' capabilities and adaptations toward bioenergy-related productivities. The green alga Chlamydomonas reinhardtii was genetically engineered to eliminate one of its major biomolecular constituents, polyglucan carbohydrates, such as starch and amylose. The purpose was to determine the possibility of reallocating fixed carbon into another basic component, fatty acid-containing lipids such as triacylglycerol (TAG). The results were mildly favorable, but partitioning was drastically altered when the ability to properly synthesize starch was reintroduced by complementation. Effects of nitrogen deprivation, a known starch- and lipid-accumulation trigger, were assessed, but significantly, complemented mutants accumulated greater amounts of both starch and storage lipid during nutrient replete cultivation than wildtype or starchless strains during nitrogen stress. This hyperaccumulation phenotype is promising for the possibility of tuning photosynthetic metabolism to the synthesis of specific molecules. The cyanobacterium Synechococcus sp. PCC 7002 was likewise modified for the interruption of glucose activation to higher glucans and was also engineered for the secretion of fatty acids. Carboxylated hydrocarbons of medium chain length such as lauric acid (C12) are drop-in fuel precursors that require minimal processing to derive the combustible product. When conferred with a C12-secreting capability, this organism dedicated 10% of its fatty acid portfolio to lauric acid, most of which was released from the cell into the culture medium without further persuasion. Though eliminating higher carbohydrates did not change the amount of C12 generated, a small increase in total fatty acyl lipids was observed. Aside from a severe decrease in reducing carbohydrate content, the most dramatic effects of removing this important pathway occurred in photosynthesis and during nitrogen deprivation. Rearrangements were observed in electron transport from photosystem II and through the plastoquinone pool, and the photoprotective abilities of this organism are illustrated by wildtype levels of O2 being generated by the inhibited strain despite a lower growth rate. When nitrogen starved, a buildup of metabolic precursors resulted in organic acids being secreted into the culture medium, which are also valuable biocommodities. Synechococcus sp. PCC 7002 is a robust platform for metabolic engineering and physiological investigation, and it may be emerging as a feedstock organism for targeted bioproducts. The task of re-engineering photosynthetic metabolism can be likened to domesticating an agricultural plant. We can begin the process, but its outcome will be dictated by the ancient biology on which it is based. The results of this work can be progressively adjusted in the pursuit of renewable and sustainable energy sources, an endeavor that appears to be a viable possibility. To those that photosynthesize, we salute you.
  • Pulsed PECVD synthesis of metal dichalcogenide thin films for sustainable energy applications

    Wolden, Colin Andrew; Sentman, Christopher; Agarwal, Sumit; Ohno, Timothy R. (Colorado School of Mines. Arthur Lakes Library, 2014)
    The current world energy demand is ~15 TW and growing, with >85% of production coming from non-renewable sources. The technologies for renewable energy exist, but to achieve this unprecedented scale of production at affordable cost will require developing alternative, earth abundant materials and develop new ways to produce them. Metal dichalcogenide (MS2, MSe2) are a class of semiconductors with unique optical, electrical and catalytic properties with potential applications in sustainability. The aim of this thesis was to develop a pulsed plasma-enhanced chemical vapor deposition (PECVD) as a novel approach for well controlled synthesis of stoichiometric thin films of FeS2 and WS2, establish their intrinsic material properties, and explore their potential in renewable energy applications. First, pulsed PECVD was developed for self-limiting growth of pyrite (cubic FeS2), a potential absorber for thin film solar cells. This material has promising attributes for photovoltaics, but poor device performance experienced to date has been attributed to the difficulty of controlling stoichiometry, avoiding marcasite phase impurities (orthorhombic FeS2), and surface defects. To mitigate these issues, several techniques rely on a post deposition sulfur annealing step, which would not be amenable for large scale manufacturing. In this work, self-limiting growth of FeS2 was accomplished using a continuous flow of Fe(CO)5 and H2S diluted in argon. The onset of thermal CVD was identified to be at ~300 °C, and films produced by thermal CVD contained sub-stoichiometric pyrrhotite. In contrast, pulsed PECVD produced stoichiometric FeS2 films without the need for post-deposition sulfurization. Films contained a mixture of pyrite and marcasite, though the latter could be minimized using a combination of high duty cycle, low temperature, and low plasma power. Conversely, marcasite rich films could be produced using low duty cycles and high plasma power. Both pyrite- and marcasite-rich films displayed similar optical properties with a band gap of ~1 eV and an absorption coefficient of ~10[superscript 5] cm[superscript -1]. Pyrite displayed relatively higher photoconductivity, but the absolute response was poor and solid-state devices fabricated with pyrite showed no rectifying behavior, indicating that this material may not be suitable for PV. Another energy application explored was the use of FeS2 as a cathode for Li batteries because of its high energy density. Here the composition was shown to have an impact. Pyrite films showed high initial discharges near 890 mA*hr/g. Similar capacities were observed initially for marcasite, but these films degenerated after a few cycles. The generality of pulsed PECVD for dichalcogenide synthesis was tested by applying the lessons gained from depositing pyrite to WS2. Stoichiometric WS2 thin films were produced by simply replacing Fe(CO)5 with W(CO)6. Films were deposited by thermal CVD and continuous wave (CW) PECVD for comparison, and it was found that pulsed PECVD delivered the best crystalline quality at combinations of high plasma power and intermediate duty cycles ([tau] = 0.50 - 0.67). This was attributed to the observation that pulsing produced transients with significantly enhanced plasma intensity relative to CW PECVD. Moreover the orientation of the films could be controlled through choice of duty cycle and thickness. WS2 was demonstrated to be catalytically active for hydrogen evolution reaction (HER), as films deposited on fluorine-doped tin oxide with an increased density of edge sites was shown to reduce the HER onset potential from 340 mV to 240 mV vs. RHE. Pulsed PECVD may also be promising for synthesizing WS2 nanocrystals, which could be formed in abundance under certain operating conditions.
  • Novel infrared spectroscopic techniques for the study of adsorbed proteins on photoactive thin films

    Furtak, Thomas E. (Thomas Elton), 1949-; Angle, Taylor Allan; Collins, Reuben T.; King, Paul W. (Colorado School of Mines. Arthur Lakes Library, 2014)
    Through the development of attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopic techniques, as well as biocompatible nanoporous gold film confining layers and photoactive nanocrystal cadmium telluride (CdTe) thin films, a system capable of in situ study of adsorbed protein films on photoactive layers was created. Due to the oxygen intolerance of the enzyme of interest for this work (a [FeFe]-hydrogenase from Clostridium acetobutylicum), techniques were developed in a manner conducive to anaerobic environments. Solid-state ligand exchange processes were shown to have no detrimental effect on the continued ability of nanocrystal CdTe layers to reduce species via the transfer of photogenerated electrons. Nanoporous gold films were shown to effectively confine poorly bound surface species including nanocrystal CdTe layers and adsorbed protein films. An ATR "stack'' structure, consisting of a silicon wafer coupled to a zinc selenide ATR crystal by a high index optical coupling fluid, was designed and implemented, leading to a tunable optical structure for use with existing ATR setups. This ATR stack was shown to maintain resolution and signal intensity of traditional ATR configurations for both aqueous and solid-state samples. Through the use of coupled silicon wafers, we significantly increased both sample throughput and the number of available chemical processes by replacing the expensive ATR crystals as the default sample substrate. Shown herein to function as initially intended, these novel methods provide the groundwork for more complex experiments, such as an in situ monitoring of the photooxidation of surface-bound hydrogenases.
  • Effect of viscosity-compressibility product variation on the analysis of fractured well performances in tight unconventional reservoirs

    Ozkan, E.; Komurcu, Caglar; Tutuncu, Azra; Thompson, Leslie (Colorado School of Mines. Arthur Lakes Library, 2014)
    This research study for a Master of Science degree has been conducted under the Unconventional Reservoir Engineering Project (UREP) at the Marathon Center of Excellence for Reservoir Studies (MCERS) in the Petroleum Engineering Department of Colorado School of Mines. The main objective of the research is to investigate the effect of pressure-dependent viscosity-compressibility product on the analysis of fractured, tight-gas well performances. Pressure drops required to economically produce fractured, tight-gas wells may be in the thousands of psi. Under these conditions, the gas compressibility-viscosity product may exhibit variations 3 to 10 times greater than the initial values in the vicinity of the fracture and have a significant impact on the observed rate-time behavior. Consequently, solutions and procedures used in conventional gas-well performance evaluation, which assume negligible variation of the viscosity-compressibility product, yield lower than expected permeability values. Further, since most of the property variation occurs very close to the fracture surface, accurately modeling their effects using finite difference methods is difficult due to severe time-step restrictions to ensure numerical stability and/or accuracy. In this research, analytical, semianalytical, and numerical models are used. The spectral solution was developed by Thompson (2014), but has not been reported earlier. It is verified and used to observe the effects of variable viscosity-compressibility product in the analysis of fractured, tight-gas well performances in this thesis. In addition, a new perturbation solution is developed to discuss the validity of the superposition time in the analysis of nonlinear, tight-gas well performances. Data obtained from a commercial simulator (Eclipse) and numerical results from existing fully analytical solutions for constant viscosity-compressibility product are used for the verification of the new solutions. A similarity solution for infinite-acting reservoirs, provided by Thompson (2014), is also used in the verifications. Comments are made on the advantages and disadvantages of the numerical solutions. The new solutions presented in this thesis demonstrate the shortcomings of the existing solutions and procedures in the analysis of fractured, tight-gas well performances. It is shown that the conventional definition of the superposition time is not accurate enough for tight-gas wells. Based on the new solutions, guidelines are provided to improve the analysis of fractured, tight-gas well performances.
  • RAFT polymerization kinetics and polymer characterization of P3HT rod-coil block copolymers and their uses to prepare hybrid nanocomposites

    Boyes, Stephen G.; Kern, Melissa Robin; Knauss, Daniel M.; Wu, David T.; Collins, Reuben T.; Posewitz, Matthew C. (Colorado School of Mines. Arthur Lakes Library, 2014)
    The purpose of this work is to provide well-defined P3HT rod-coil block copolymer systems that can form self-assembled structures and be used as templates for the preparation of P3HT hybrid nanocomposites. To this end, a new P3HT macroRAFT agent was designed such that the P3HT was incorporated into the R group rather than the Z group which, in addition to providing a useful end group functionality, allows for a true 'grafting from' approach when preparing rod-coil block copolymers. The prepared P3HT macroRAFT agent is extensively characterized by proton nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) with a focus on an understanding of the limitations of each technique for molecular weight characterization and gaining insight into the efficiency of end-group reactions as both of these factors affect the composition of the subsequently prepared block copolymers. The RAFT polymerization kinetics of the coil blocks, namely poly(styrene) and poly(tert-butylacrylate) were followed in order to demonstrate the effectiveness of the P3HT macroRAFT agent and gain insight into the polymer composition. Direct quantification of the RAFT polymerization is necessary to obtain reproducible block copolymers with predictable molecular weights and narrow molecular weight distributions and yet an in-depth analysis of the RAFT polymerization kinetics is lacking in prior reports. Again, comprehensive characterization of the block copolymers is used to present a more realistic representation of the block copolymer sample. It is purposed that 1H NMR provides the most accurate molecular weight and composition data, although there is a slight overestimation due to inefficient end-capping reactions. However, by combining MALDI-TOF end-group analysis with 1H NMR data, some understanding of the amount of overestimation is achieved. This is particularly important as inefficient end group reactions result in P3HT homopolymer in the final sample. Therefore accurate characterization requires molecular weight determination of the block copolymer and quantification of the sample composition. Also presented in this work is the synthesis of amphiphilic rod-coil block copolymers of P3HT with poly(4-vinyl pyridine) (4VP) and poly(acrylic acid) (AA). Here, P3HT-b-PAA is prepared by the direct synthesis of acrylic acid with the macroRAFT agent using a binary solvent system of trichlorobenzene and dioxane to maintain polymer solubility throughout the polymerization. The micelle formation of the resulting block copolymer is detailed as the transparent micelle solution of P3HT-b-PAA exhibits the optical behavior of solid-state P3HT. Finally, the preparation of various nanocomposites from the synthesized P3HT homopolymer and block copolymers is presented. In the first method, the RAFT end group of the P3HT macroRAFT agent and the P3HT block copolymers is reduced to a thiol to allow for attachment to Au nanoparticles. While Au nanoparticles are not useful for photovoltaic applications, the surface modification demonstrates the utility of the P3HT macroRAFT agent, which is used to modify the surface with P3HT homopolymer and P3HT block copolymers. The second method to prepare P3HT hybrid nanocomposites is in-situ growth of CdS in P3HT-b-P4VP. With analysis by dynamic light scattering (DLS), Fourier-transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM), it is concluded that a majority of the CdS growth in the P3HT-b-P4VP was confined to the P4VP block.
  • Engineering the surfaces of group IV materials for energy applications

    Agarwal, Sumit; Stradins, Pauls; Chaukulkar, Rohan P.; Ciobanu, Cristian V.; Wolden, Colin Andrew; Wu, Ning (Colorado School of Mines. Arthur Lakes Library, 2014)
    A majority of our energy needs today is met by fossil fuels. The combustion of fossil fuels leads to the release of greenhouse gases which adversely affect our environment. This has prompted significant efforts to harness the various sources of renewable energy available to us. Solar energy is the only source of renewable energy capable of meeting our ever-increasing energy demands. Of the various solar technologies, photovoltaic (PV) technology promises to be an attractive option for the generation of electricity due to no emissions of greenhouse gases and various additional socio-economic benefits. A major obstacle in the implementation of PV technology on a large scale is the cost. This has led to an increased interest in research directed towards reducing the cost of electricity generated through PV. Si based PV holds majority of the market share. Therefore, a major challenge in the field of PV is the reduction of cost of electricity generated via Si based PV technologies. This goal can be achieved by the development of high-efficiency solar cells based on Si. Surface passivation is one of the reasons often cited for low efficiencies observed in solar cells. Hence, as a part of the work completed in this dissertation, we have studied the surface passivation in c-Si solar cells. Specifically, we have used infrared spectroscopy techniques and minority carrier lifetime measurements to study the mechanism of surface passivation of c-Si by Al2O3. The passivation of the Si surface via Al2O3, deposited by atomic layer deposition (ALD), is achieved by a reduction in the defect density at the interface (D[subscript it]) (chemical passivation) and an increase in the fixed negative charge (Q[subscript f]) associated with the Al2O3 films (field effect passivation). A post-deposition annealing step is required to achieve this high level of passivation. We have investigated the effect of the annealing step in order to understand the mechanism of chemical passivation. Specifically, we have studied the role of H and O in the chemical passivation of c-Si by Al2O3. Our results indicate that it is the restructuring at the interface, and not the migration of H from Al2O3 to the c-Si interface, that contributes to the reduction in the interface defect density. In addition to Al2O3, TiO2 has also been proposed as a surface passivant for c-Si. TiO2, due to its optical properties, has the added advantage of acting as an anti-reflection coating in addition to the surface passivation. Atomic layer deposition (ALD) technique is often used to deposit these TiO2 thin films. However, the low growth per cycle observed for typical ALD processes makes it unfeasible to be used on a large scale. Therefore, we have developed a novel ALD chemistry for the deposition of TiO2 with a high growth per cycle. We use a metal alkoxide metal-chloride precursor combination to deposit the TiO2 thin films wherein the metal-alkoxide acts as the oxygen source. We have used in situ IR spectroscopy to study the surface reaction mechanism during the deposition process. We found that the reaction follows a alkyl-tranfer mechanism over the range of 150-250 °C. The use of metal-alkoxide as the oxygen source would also potentially mitigate the problem of interfacial oxide formation and hence, enable deposition of TiO2 on oxygen sensitive substrates. Renewable energy sources such as solar energy, have an intermittent nature which increases the importance of an efficient energy storage system. Due to their high energy and power density, low self-discharge and maintenance, lithium-ion batteries (LIBs) are attractive candidates to meet this challenge. However, the LIB technology needs significant improvements before it can be implemented as an effective storage system. One of the factors which would improve the capacity of the LIB is the anode material. Group IV materials such as Si, Ge and Sn, all have higher capacities than the current conventional anode material, graphite. The use of these materials as anodes in LIBs is however unfeasible due to the significant volume expansion these materials undergo upon lithiation. The volume expansion leads to electrode pulverization and a loss in battery capacity after just the first few charging and discharging cycles. A way to circumvent this issue is the use of nanomaterials. Specifically, carbon-coated Group IV nanomaterials have shown enhanced capacities as compared to graphite. To this end, we have developed a single-step technique to synthesize carbon-coated Si, Ge, and Sn nanoparticles. In this technique, we use two non-thermal plasmas in series to first synthesize the nanoparticles, and then coat them with carbon. We have studied the effects of varying the plasma parameters on the nature of the coating we employ on these nanoparticles. We have shown that the use of two plasmas allow us to independently control the synthesis and coating of these nanoparticles. Efficient use of energy also contributes to the reduction of fossil fuel emissions. Artificial lighting consumes a significant portion of the electricity we generate. Hence the use of LEDs, which have been shown to be more efficient that traditional lighting sources, can greatly impact the fossil fuel emissions. Silicon carbide, due to its high band-gap has been proposed as a material for the manufacture of blue LEDs. The use of nanomaterials has been shown to enhance the luminescence properties of silicon carbide. Therefore, as a part of the work completed in this dissertation we propose a low-temperature technique to synthesize silicon carbide nanoparticles. We use a dual-plasma setup similar to the one used to synthesize the carbon-coated Group IV nanoparticles. The Si nanoparticles are synthesized in the upstream plasma and then carburized in the downstream plasma to form crystalline silicon carbide nanoparticles.
  • Efficient reconstruction of a multiscale refractive index, An

    Ganesh, Mahadevan; Cabell-Kluch, Thomas; Rhoadarmer, Troy; Tenorio, Luis (Colorado School of Mines. Arthur Lakes Library, 2014)
    The ability to accurately correct for the effects of strong atmospheric turbulence on light has been a major area of research in astronomy and adaptive optics. Atmospheric turbulence induces an optical region with inhomogeneous refractive index. The main focus of this research is to efficiently reconstruct the refractive index using observed/simulated optical phase aberrations. Our method is based on the tomography associated with these aberrations. In this work, assuming the turbulent atmosphere is of Kolmogorov type, we extend the range of the reconstruction. We demonstrate the approach for simulated data from an astronomy model. The limitations of the process are explored to determine a required range of parameters to reconstruct an accurate solution. The method is tested against increasing refractive index aberrations and imaging scenarios. In addition, the method is parallelized and optimized and its parallel performance is characterized. Parallel performance is characterized for CPU systems as well as for heterogeneous computing environments comprising of GPUs and CPUs.
  • Rock fall mitigation for an open pit mine experiencing substantial rock fall from overblasting

    Higgins, Jerry D.; Cybulski, Paige G.; Lupo, John F.; Santi, Paul M. (Paul Michael), 1964- (Colorado School of Mines. Arthur Lakes Library, 2014)
    Rock fall is a common hazard in open pit mines causing safety concerns for workers, transportation routes and may adversely affect mine production. To reduce and mitigate rock fall hazards, a benched slope design is normally used and, occasionally, additional mitigation may be necessary in areas with excessive rock fall hazards. Newmont's Boddington Gold Mine in Australia is experiencing substantial rock fall in the south portion of their open pit mine due to rock damage from blasting resulting in highly fractured wall rock. This has increased the volume of rock fall experienced in the mine, and the rock fall has caused accumulation of debris on benches and crest loss, reduced bench width, in some parts of the mine by as much as 40 percent. The loss of bench width has reduced the effectiveness of the benches for rock fall mitigation and allowed rock fall to travel much farther down slope than desired for safety. Because of these conditions, there is a 20 meter exclusion zone near the rock walls in the mine, reducing production and impairing safety conditions. The mine is currently mitigating the rock fall by draped mesh, spot bolts, cable lashing and benches originally excavated at 8 meters in width. As the open pit is deepened, a more permanent rock fall mitigation method is desired. Newmont proposed several modified bench designs to be evaluated. The new bench designs were evaluated by modeling rock fall on the existing and proposed bench designs using the Colorado Rock Fall Simulation Program (CRSP) and RocFall. Newmont provided rock fall data for modeling that included the normal coefficient of restitution and rock fall video from the open pit. Rock fall kinetic energies, bounce heights and velocities on existing benches and proposed benches were examined on five cross-sections from the open pit to assess which bench design had the most efficient rock fall mitigation. The importance of testing the normal coefficient of restitution and use of rock fall video for rock fall modeling were also examined, as well as the slope steepness versus rock fall run out with the new bench designs.
  • Amplitude inversion of fast and slow converted waves for fracture characterization of the Montney Formation in Pouce Coupe field, Alberta, Canada

    Davis, Thomas L. (Thomas Leonard), 1947-; MacFarlane, Tyler L.; TSvankin, I. D.; Benson, Robert D.; Grossman, Jeff (Colorado School of Mines. Arthur Lakes Library, 2014)
    The Montney Formation of western Canada is one of the largest economically viable gas resource plays in North America with reserves of 449TCF. As an unconventional tight gas play, the well development costs are high due to the hydraulic stimulations necessary for economic success. The Pouce Coupe research project is a multidisciplinary collaboration between the Reservoir Characterization Project (RCP) and Talisman Energy Inc. with the objective of understanding the reservoir to enable the optimization of well placement and completion design. The work in this thesis focuses on identifying the natural fractures in the reservoir that act as the delivery systems for hydrocarbon flow to the wellbore. Characterization of the Montney Formation at Pouce Coupe is based on time-lapse multicomponent seismic surveys that were acquired before and after the hydraulic stimulation of two horizontal wells. Since shear-wave velocities and amplitudes of the PS-waves are known to be sensitive to near-vertical fractures, I utilize isotropic simultaneous seismic inversions on azimuthally-sectored PS[subscript 1] and PS[subscript 2] data sets to obtain measurements of the fast and slow shear-velocities. Specifically, I analyze two orthogonal azimuths that are parallel and perpendicular to the strike of the dominant fracture system in the field. These volumes are used to approximate the shear-wave splitting parameter that is closely related to crack density. Since crack density has a significant impact on defining the percolation zone, the work presented in this thesis provides information that can be utilized to reduce uncertainty in the reservoirs fracture model. Isotropic AVO inversion of azimuthally limited PS-waves demonstrates sufficient sensitivity to detect contrast between the anisotropic elastic properties of the reservoir and is capable of identifying regions with high crack density. This is supported by integration with spinner production logs, hydraulic stimulation history of the field, and microseismic. Results also show significant fracture network heterogeneity that is not typically accounted for in engineering-driven development despite a strong link to production. The main value of this work lies in the integration of fracture characterization with preceding RCP theses that defined the geomechanical model and composition of the reservoir at Pouce Coupe. Geophysical attributes that relate to the composition and natural fractures enable a more complete understanding of the reservoir and indicate that a successful well is dependent on both the hydrocarbon storage capacity of the matrix and a large permeable network of natural fractures.
  • Development of experimental methods for intermediate scale testing of deep geologic CO2 sequestration trapping processes at ambient laboratory conditions

    Illangasekare, T. H.; Vargas-Johnson, Javier; Pini, Ronny; Benson, David A. (Colorado School of Mines. Arthur Lakes Library, 2014)
    Carbon Capture and Storage (CCS) is a potential strategy to reduce CO2 emissions into the atmosphere. Deep geological formations provide a viable storage site for significant amounts of CO2, however their depth from the surface and extreme conditions make planning and monitoring a CCS project difficult. Improved knowledge of the fundamental processes involved in trapping of CO2 in naturally heterogeneous deep saline aquifers in an efficient and safe manner is beneficial for present and future projects. Understanding and study of these processes under controlled conditions in field settings is not feasible. As an alternative, this study developed and experimental methods to study capillary and dissolution trapping processes at ambient laboratory conditions using analog fluids in place of supercritical CO2 (scCO2) and brine. These experimental methods allow measuring and analyzing the effects of heterogeneity on carbon sequestration at larger laboratory scales than previously done. The results of these types of experiments help researchers develop improved models and test them for better project design and performance assessment in the field for storage permanence. These experiments include tests that obtain the constitutive relationships of capillary pressure and relative permeability, injection of scCO2 into a 2D-confined aquifer that uses an x-ray attenuation technique to precisely track the plume and measure trapping saturations, and an intermediate scale experiment of dissolution fingering that will form the base for future experiments seeking to understand dissolution trapping in formations with low permeability zones. Strategies to accurately model the intermediate scale capillary trapping experiment using T2VOC were also developed.
  • Analysis of diesel particulate matter using electron monochromator-mass spectrometry, bacterial identification using mass spectrometry and lateral flow immunochromatography, and detection of levamisole as a cutting agent in patients using cocaine

    Voorhees, Kent J.; Jensen, Kirk Richard; Posewitz, Matthew C.; Marr, David W. M.; McCormick, Robert L.; Eberhart, Mark E. (Colorado School of Mines. Arthur Lakes Library, 2014)
    Three studies and one review involving analytical mass spectrometry and one article on rapid bacterial diagnostics are presented herein. Electron monochromator-mass spectrometry (EM-MS) literature is presented outlining the development history and relevant analytical applications including nitro compounds in cigarette smoke, resonance energy studies, explosives, and bacterial identification. Diesel particulate matter and the effect of antioxidant fuel additives on nitro polycyclic aromatic production during diesel engine operation was investigated using EM-MS. Results showed a strong correlation between production of 2,6-di-tert-butyl-4-nitrophenol (DBNP) and the addition of two antioxidant precursors to the fuel prior to combustion. No correlations were observed between DBNP production and engine load or speed. Results indicate that the role of fuel additives in combustion byproducts must be carefully considered. When using CaO as a matrix-replacement in matrix-assisted laser desorption/ionization mass spectrometry, fatty acids are cleaved from phospholipids in situ by laser-induced pyrolysis. Ten bacterial genera were investigated using CaO as a matrix. Fatty acid profiles were observed and exported for statistical analysis. Principal components analysis of fatty acid profiles revealed distinct separation of bacterial genera. Cross-validation resulted in greater than 94% correct assignment. Future applications could provide clinicians a rapid and reliable method of bacterial detection. Outbreaks of infectious bacteria and concerns over bioterrorism have increased the demand for methods of rapidly and easily detecting bacteria. A lateral flow immunoassay (LFI) device was developed to detect Bacillus anthracis indirectly by using gamma phage amplification. Phage-based LFI detection of B. anthracis Sterne was consistently observed within four and as little as two hours of the onset of phage amplification with a threshold sensitivity of 2.5 x 10[superscript 3] cfu/mL. Ease and speed of the device could find application in the field by military personnel. Finally, individuals admitted to a hospital following cocaine use showed symptoms of levamisole poisoning. Levamisole, an antihelminthic used in veterinary science and a known lacing/cutting agent for cocaine, was detected in urine samples from these patients. Tissue and blood samples were also analyzed, but no concentration was detected. While no direct correlation could be made between patient symptoms and levamisole, its presence in their urine is a strong indication that the cocaine had been cut/laced with levamisole.
  • Cuttings transport implications for drill string design: a study with computational fluid dynamics

    Eustes, Alfred William; Dykes, Gregory B.; Yin, Xiaolong; Tutuncu, Azra (Colorado School of Mines. Arthur Lakes Library, 2014)
    Modern drilling programs require a variety of drilling equipment over a variety of well paths. Changes in equipment and parameters greatly affect the process of cuttings transport in the wellbore. While extensive experimental work has explored a multitude of drilling parameters, a firm methodology for using computational fluid dynamics to model this process has not been established. Moreover, computational models more easily compare different drilling geometries than experimental apparatuses that require significant equipment exchange. This thesis first establishes a methodology for utilizing computational fluid dynamics to model cuttings transport in a drilling annulus. The results establish qualitatively comparable results to prior experimental work. Therefore, the tool is made useful by isolating and studying the effects of changing parameters. The second part of the thesis consists of a parameter study to determine effects of drill pipe rotation, drilling fluid velocity, drill pipe eccentricity, wellbore inclination, and rate of penetration on cuttings accumulation over different drill pipe and borehole sizes. Results include both individual parameter effects as well as combined effects of the parameters in a single scenario, some of which suggest more complex mechanisms of cuttings transport than previously postulated.
  • Fractional diffusion in naturally fractured unconventional reservoirs

    Ozkan, E.; Ozcan, Ozlem; Tutuncu, Azra; Raghavan, R.; Sarak, Hulya (Colorado School of Mines. Arthur Lakes Library, 2014)
    The objective of the research presented in this Master of Science thesis is to examine the concept of anomalous diffusion as an alternative to the conventional dual-porosity idealizations used to model the stimulated reservoir volume (SRV) around fractured horizontal wells in tight, unconventional reservoirs. The motivation is the recent skepticism about the applicability of dual-porosity models to fractured reservoirs due to the scale and discontinuity of the fractures and the complexity of the heterogeneous, nano-porous matrix and the increased awareness of the promises of fractional derivatives in representing anomalous diffusion in highly heterogeneous porous media. A trilinear, anomalous-diffusion (TAD) model has been developed for fractured horizontal wells surrounded by an SRV in this work and compared with the existing trilinear, dual-porosity (TDP) model. The trilinear flow model is used because of its relative simplicity and availability for the dual-porosity idealization, which allows a direct comparison. The work includes the analytical solution of a general, 1D time-fractional diffusion equation for a bounded system and the implementation of the new solution in the trilinear model formulation for the fractured inner reservoir. Numerical evaluation of the solution has been performed by a computational code in Matlab. The differences, shortcomings, and advantages of both models are discussed. The application of the models to field data is also demonstrated. A discussion of the characteristics of the pressure and derivative responses obtained from the TAD model is also provided and related to the fractal nature of fractured media. Physical interpretations are also assigned to fractional derivatives and the phenomenological coefficient of the fractional flux law. It is shown that the anomalous diffusion formulation does not require explicit references to the intrinsic properties of the matrix and fracture media and thus relaxes the stringent requirements used in dual-porosity idealizations to couple matrix and fracture flows. The trilinear anomalous-diffusion model should be useful for performance predictions and pressure- and rate-transient analysis of fractured horizontal wells in tight unconventional reservoirs.
  • Modeling flow in nanoporous, membrane reservoirs and interpretation of coupled fluxes

    Ozkan, E.; Geren, Filiz; Tutuncu, Azra; Firincioglu, Tuba (Colorado School of Mines. Arthur Lakes Library, 2014)
    The average pore size in unconventional, tight-oil reservoirs is estimated to be less than 100 nm. At this pore size, Darcy flow is no longer the dominating flow mechanism and a combination of diffusive flows determines the flow characteristics. Concentration driven self-diffusion has been well known and included in the flow and transport models in porous media. However, when the sizes of the pores and pore-throats decrease down to the size of the hydrocarbon molecules, the porous medium acts like a semi-permeable membrane, and the size of the pore openings dictates the direction of transport between adjacent pores. Accordingly, characterization of flow and transport in tight unconventional plays requires understanding of their membrane properties. This Master of Science thesis first highlights the membrane properties of nanoporous, unconventional reservoirs and then discusses how filtration effects can be incorporated into the models of transport in nanoporous media within the coupled flux concept. The effect of filtration on fluid composition and its impact on black-oil fluid properties like bubble point pressure is also demonstrated. To define filtration and filtration pressure in unconventional, tight-oil reservoirs, analogy to chemical osmosis is applied two pore systems connected with a pore throat, which shows membrane properties. Because the pore throat selectivity permits the passage of fluid molecules by their sizes, given a filtration pressure difference between the two pore systems, the concentration difference between the systems is determined by flash calculations. The results are expressed in the form of filtration (membrane) efficiency, which is essential parameter to define coupled fluxes for porous media flow.
  • Cross-polarized wave generation (XPW) for ultrafast laser pulse characterization and intensity contrast enhancement

    Durfee, Charles G.; Iliev, Marin; Squier, Jeff A.; Kowalski, Frank V.; Wakin, Michael B. (Colorado School of Mines. Arthur Lakes Library, 2014)
    Good pulse quality, high peak power and tunable central wavelength are amongst the most desired qualities in modern lasers. The nonlinear effect cross-polarized wave generation (XPW), can be used in ultrafast laser systems to achieve various pulse quality enhancements. The XPW yield depends on the cube of the input intensity and acts as a spatio-temporal filter. It is orthogonally polarized to the input pulse and highly Gaussian. If the input pulse is well compressed, the output spectrum is smoother and broader. These features make XPW an ideal reference signal in pulse characterization techniques. This thesis presents a detailed analysis of the XPW conversion process, and describes novel applications to pulse characterization and high-quality pulse cleaning. An extensive computer model was developed to describe XPW generation via solution of the full coupled non-linear differential equations. The model accounts for dispersion inside the nonlinear crystal and uses split-step Fourier optics beam propagation to simulate the evolution of the electro-magnetic fields of the pump and XPW through free-space and imaging systems. A novel extension to the self-referenced spectral interferometry (SRSI) pulse characterization technique allows the retrieval of the energy and spectral content of the amplified spontaneous emission (ASE) present in ultrashort pulse amplifier systems. A novel double-pass XPW conversion scheme is presented. In it the beam passes through a single XPW crystal (BaF2) and is re-imaged with a curved mirror. The technique resulted in good (~30%) efficiency without the spatial aberrations commonly seen in another arrangement that uses two crystals in succession. The modeling sheds light on the complicated nonlinear beam dynamics of the double-crystal conversion, including self- and cross-phase modulation, self-focusing, and the effects of, relative on-axis phase-difference, relative beam sizes, and wave-front curvature matching on seeded XPW conversion. Finally, a design is presented for exploiting the clean-up properties of XPW at the output of an optical parametric generation (OPA) setup in conjunction with an extremely compact prism compressor. The prisms material, separation and geometry are designed carefully to work at the correct wavelength of the OPA setup and are extrapolated to accommodate wavelengths, such as 2[mu]m of parametric wave generation.
  • On metastable nitrides with potential renewable energy applications

    Richards, Ryan; Caskey, Christopher Michael; Yang, Yongan; Williams, S. Kim R.; Yang, Yuan; Ginley, D. S. (David S.); Ciobanu, Cristian V. (Colorado School of Mines. Arthur Lakes Library, 2014)
    This thesis explores some of the lesser-studied materials in the metal nitride family, copper nitride (Cu3N), two tin nitrides (Sn3N4 and SnN) and antimony oxynitride, via high-throughput combinatorial methods. Copper nitride was investigated as a potential photovoltaic absorber material. Stable, phase pure Cu3N thin films were grown on glass substrates at temperatures between 150 and 200°C, depending on the target-substrate distance. The analysis of the synthetic results provides insights into the thermodynamic origins of the growth of metastable Cu3N, and sets a nitrogen chemical potential of +1 eV/atom as a lower limit of the anion activity that can be achieved in non-equilibrium thin film growth of metastable materials. The semiconducting properties of tin nitride are explored by thin-film experiments and first-principles theory to evaluate the efficacy of this material for optoelectronic technologies. A computational study of related group IV nitride polymorphs provides additional insight into the properties and challenges associated with this class of semiconductors. We report the first binary crystalline nitride containing Sn(II), a semiconductor having composition near SnN. The material has a band gap between 1.5 and 2 eV, and n-type conductivity arising from 10^20 carriers/cm^3 with mobility of 2 cm^2/Vs. Finally, we report the relatively unknown antimony oxynitride, which we prepare by reactive sputtering and measure its bulk stoichiometry for the first time. The oxynitride thin films have approximate composition Sb3O3xN5-2x, where x is near 0.4. The films are resistive, have an optical absorption onset near 2 eV, and have low long-range order. The stability of the films was found to be dependent on the growth temperature, with films grown at ambient temperature being shelf-stable while films grown at elevated temperatures converted to the oxide.
  • Adsorption characteristics of polymer electrolyte membrane chemical degradation products and their impact on oxygen reduction reaction activity for platinum catalysts

    Richards, Ryan; Christ, Jason M.; Ciobanu, Cristian V.; Williams, S. Kim R.; Yang, Yongan; Yang, Yuan; Dinh, Huyen N. (Colorado School of Mines. Arthur Lakes Library, 2014)
    Developments in membrane-electrode assembly and stack technology have significantly improved the performance of polymer electrolyte membrane fuel cells; such that systematic studies focused on improving major challenges of overall cost and durability have become increasingly important. Consequently, interest in the examination of system derived impurities and their subsequent effects on performance durability has grown. Studies involving commercial polymer electrolyte membranes and model compounds have shown that when perfluorinated sulfonic acid (PFSA) membranes are exposed to hydroxyl radicals during fuel cell operating conditions, several chemical decomposition products can be generated. Along with losses in membrane conductivity and structural integrity, such PFSA membrane degradation products may also adsorb on the platinum based electrocatalyst, possibly leading to a loss in catalyst electrochemical surface area (ECA), oxygen reduction reaction (ORR) activity, or both. This work investigates adsorption characteristics and effects from model compounds in the forms of fluorinated organic acids, representing PFSA membrane chemical degradation species, on ECA and ORR activity for platinum based electrocatalysts including polycrystalline Pt, high surface area carbon supported Pt, and extended surface Pt. A reproducible method was developed in order to investigate surface coverage and adsorption properties due to carboxylate and sulfonate functional groups, fluorocarbon chain length, and model compound concentration. Data was obtained using a variety of electroanalytical techniques including mainly cyclic and linear sweep voltammetry, and electrochemical quartz crystal microbalance analysis. Information gleaned from this work shows that reversible adsorption occurs initially through carboxylate anions, while intermolecular forces involving fluorocarbon chain length and ether and sulfonate moieties play a secondary role in molecular ordering at the electrode surface. Reversible losses in Pt electrocatalyst activity in regards to the ORR were realized most heavily for diacid compounds (greater than 44% loss in kinetic current) containing both carboxylate and sulfonate functional groups, followed by longer chain fluorinated carboxylic acids (17% loss in kinetic current). Fluorinated sulfonic acids and shorter chain carboxylic acids showed little to no effects on ORR activity at the concentrations (0.001 mM - 1 mM) studied.

View more