2024 - Mines Theses & Dissertations

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  • Publication
    Investigation on the paint baking effect in resistance spot welds of advanced high strength steels, The
    (Colorado School of Mines. Arthur Lakes Library, 2024) Marshall, David V.; Speer, J. G.; Findley, Kip Owen; De Moor, Emmanuel; Gockel, Joy
    One approach automakers take to improve vehicle fuel efficiency is to reduce vehicle mass, which requires steels with improved strength and toughness compared to conventional steels. Over the past few decades, steel researchers have engineered the third generation (Gen3) of advanced high strength steels (AHSSs) that exhibit improved strength and toughness relative to first generation (Gen1) AHSSs at a decreased cost relative to second generation AHSSs. Though Gen3 steels have been successfully developed, their implementation in automotive assembly has been limited by challenges in resistance spot welding, the most commonly used joining technique in the automotive industry. Gen3 spot weld mechanical properties are often insufficient in comparison with those of Gen1 spot welds, though it has been observed that the automotive paint-baking cycle can mitigate this insufficiency. The microstructural evolution associated with these baking-induced improvements is not fully understood, which highlights the area of research this thesis seeks to address. The purpose of this study was to investigate the effects of the paint-baking cycle (180 °C, 20 min) on Gen1 and Gen3 spot weld microstructures and mechanical properties and to understand the origin of the differences in their baking sensitivities. A new specimen geometry coupled with digital image correlation was implemented and revealed greater plastic strains were measured within the heat-affected zone (HAZ) of baked welds compared with unbaked welds. Subsequent experiments were developed to isolate the different HAZ microstructures to quantify the baking sensitivities of each by implementing the small punch test method. Small punch test results identified a trough in energy absorption within the intercritical HAZ of the Gen3 steel that was mitigated after paint baking. The Gen1 HAZ microstructures were characterized by a minor sensitivity to baking and the absence of an intercritical trough in energy absorption. Thermocouple measurements taken during Gleeble®-simulation of HAZ microstructures confirmed depression of the martensite start (MS) temperature with decreasing intercritical temperature, and this effect was more prominent in the Gen3 steel. To elucidate the differences in Gen1 and Gen3 spot weld baking sensitivities, a carbon diffusion distance model was developed that predicted the greatest fraction of baking-sensitive martensite would form in the intercritical HAZ of the Gen3 spot welds. 3D atom probe tomography conducted on Gen3 spot weld HAZ microstructures identified carbon redistribution in twinned martensite regions in the intercritical HAZ and carbon segregation to martensite lath boundaries in the supercritical HAZ of baked specimens. The intercritical HAZ was concluded to be a baking critical microstructure regarding Gen3 spot weld baking sensitivity, and this represents a new finding in the field of research on AHSS spot welds. The insensitivity of the DP spot welds to baking is proposed to be due to the higher MS temperature through the intercritical HAZ, enabling carbon redistribution during cooling of the weld that is not possible in Gen3 spot welds.
  • Publication
    Commercialization of space resources: financing the next wave of investment in space resources, The
    (Colorado School of Mines. Arthur Lakes Library, 2024) Janikowski, Adam A.; Lange, Ian; Malone, Aaron; Abbud-Madrid, Angel; Sowers, George
    The opportunity and potential in developing space resources is enormous, with estimates for a medium-term space resources economy in the trillions of dollars. Even now, the world is seeing a dramatic increase in the number of private companies focused on the exploitation of space resources, a trend that will only increase. This dissertation attempts to bring academic rigour to the study of the financing of space resources, specifically researching the current status of space resources, the financial impact of domestic space resources legislation, and the issue of establishing a multilateral development bank focused on developing space resources. The findings in these studies indicate that the financing of space resources is a complex and multifaceted issue that demands innovative approaches and collaborations between various stakeholders, including international cooperation. However, given the right approach to innovation and to funding, space resources can be harnessed for the benefit of humanity, ensuring a sustainable and prosperous future for generations to come.
  • Publication
    Energy models: dispatch and market impacts
    (Colorado School of Mines. Arthur Lakes Library, 2024) Hood, Karoline M.; Newman, Alexandra M.; Jackson, Gregory
    Optimization plays a crucial role across various facets of renewable and clean energy dispatch, mitigates the impacts of individual component failures, and incorporates additional services into dispatch models. Ultimately, these capabilities can address the impacts of design and dispatch models in varying socioeconomic settings. Many energy optimization models incorporate aspects of energy planning such as equipment inventory value, lead time, service costs, and health. Our study involves the lifespan analysis of heat exchangers within a concentrated solar power (CSP) plant. We model their thermal profiles, thermal-mechanical stresses, and fatigue using a reduced-order model and a fatigue damage tool. Our findings reveal that the evaporator's lifespan is 17.5 years, and the superheater's lifespan is 11 years, in contrast to an assumed design expectancy of 30 years. The primary cause of the failures is thermal stress in the tubesheets, which is consistent with industry reports. We utilize these updated lifespans to evaluate the gross revenue impact via simulation and optimization, and provide more realistic estimates of lead times than previously invoked. We observe a 3-4% decrease in gross revenue compared to original lifespan estimations. Hidden costs include equipment replacement and the possibility of losing a prior purchase agreement. Subsequently, our focus shifts to extending a CSP plant dispatch model to illustrate the benefits of incorporating an ancillary service, such as spinning reserves, which aid in maintaining grid reliability by requiring a 10-minute response time for a duration of two hours. The addition of this capability to a CSP plant's operation results in an annual profit increase of 3-7% across three distinct markets compared to its operation in the absence of this type of market. Lastly, we expand our investigation to assess the health impacts on socially vulnerable communities when the central grid fails. During power outages when microgrids are invoked to maintain power supply, a trade-off emerges between costs and energy demand satisfaction that disproportionately affects vulnerable communities reliant on medical devices. In addition, we evaluate the trade-offs between emissions reductions and costs, noting that more vulnerable communities experience higher mortality rates from particulate matter. When 80% of demand is met during an outage, only approximately 2% of the population is impacted by not having access to power for medical devices; but, meeting demand incurs a significant cost (i.e., a 25% increase in cost for an 80% satisfaction of demand during an outage). Conversely, the cost increases by approximately 1% with a reduction in emissions of 1% and 5%, resulting in a 4-9% reduction in mortality rates.
  • Publication
    Low temperature formic acid decomposition pathways on supported palladium nanoparticles
    (Colorado School of Mines. Arthur Lakes Library, 2024) Schlussel, Sierra; Kwon, Stephanie; Wolden, Colin Andrew; Gómez-Gualdrón, Diego A.
    Formic acid (HCOOH) has emerged as a promising liquid hydrogen (H2) carrier due to its low toxicity, low flammability, and ease of handling. The utilization of HCOOH as a potential liquid H2 carrier requires a catalytic system that selectively dehydrogenates HCOOH at low temperatures without forming any dehydration products (CO) that can act as a poison for Pt electrodes in fuel cell applications. Pd-based catalysts are widely studied for this reaction due to its high reactivity at low temperatures. Yet, details of the reaction pathways and intermediates of HCOOH dehydrogenation on Pd-based catalysts have remained inconclusive. The catalytic stability and selectivity of Pd nanoparticles have remained controversial in current literature. This work combines kinetic, isotopic, and spectroscopic methods to investigate the viability, reaction mechanism, and particle size effects of Pd/SiO2 catalysts for HCOOH decomposition pathways. In doing so, we show that supported Pd catalysts are highly active and selective towards the dehydrogenation products (H2/CO2) at low temperatures (≤383 K) without any detectable formation of dehydration products (H2O/CO). No apparent deactivation was observed up to 60 ks time-on-stream. In-situ infrared spectra measured at a range of HCOOH pressures (0.17-3.36 kPa; 353 K) detected molecularly bound HCOOH (HCOOH*) as the reaction intermediate. Such results contradict the formation of carboxylates (COOH*) and/or formates (HCOO*) that have been proposed as reactive intermediates in literature. Additional kinetic studies showed that the reaction followed a first-order reaction at low HCOOH pressures, which transitioned into zerothorder reaction at higher pressures. Isotopic studies with DCOOH and HCOOD show that both the cleaving of the O-H and C-H bonds are kinetically relevant steps. The change in Pd loading on the SiO2 support showed the importance of particle size on the rate of reaction. The smaller the particles, the more reactive they are, allowing for higher turnover rates. The results from this study can be utilized to provide design strategies for Pd-based catalysts for their use in HCOOH dehydrogenation reactions for its potential use as a liquid H2 carrier at industrial scale.
  • Publication
    Structural basis and evolutionary origins of psilocybin biosynthesis, The
    (Colorado School of Mines. Arthur Lakes Library, 2024) Hudspeth, Jesse D.; Domaille, Dylan; Cash, Kevin J.; Holz, Richard C.; Trewyn, Brian
    Psilocybin is the principal natural product of Psilocybe and other fungal genera, collectively referred to as “magic mushooms”.Therapeutic evaluation of psilocybin has revealed a remarkable potential to treat a variety of psychological conditions, including major depressive disorder, substance dependence, and end-of-life anxiety. As a result, psilocybin has received “breakthrough therapy” status by the US Food and Drug Administration and is currently the subject of 22 clinical trials. The rising interest in potential medical applications has prompted efforts to produce psilocybin biotechnologically, as well as to explore the properties of novel analogs. Four enzyme-encoding genes required for the biosynthetic pathway from L-tryptophan to psilocybin were recently identified in Psilocybe cubensis (P. cubensis) and other species, paving the way for large-scale heterologous production in microorganisms. Although heterologous production of psilocybin has been achieved, production of psilocybin analogs requires detailed characterization of the enzymes involved to optimize their activity on non-native substrates. The final reaction in the psilocybin biosynthetic pathway is catalyzed by PsiM, an S-adenosyl-L-methionine (SAM) dependent methyltransferase. This enzyme carries out the final two methylations to produce the tertiary amine psilocybin. It exhibits strict substrate specificity toward its native substrate as indicated by low to no turnover of analogous substrates. However, the pertinent structural features and subsequent mechanistic implications for specificity of PsiM have not been identified. To address these fundamental gaps in our understanding of the last step in the biosynthesis of psilocybin, we structurally and biochemically characterized PsiM from P. cubensis. Using X-ray crystallography, we achieved sub-angstrom resolution of the first crystal structures of PsiM in all stages of its reaction cycle revealing geometric restraints that dictate activity and selectivity. We also include a full kinetic characterization of PsiM toward its primary amine substrate and the monomethylated intermediate. Inspection of the secondary sphere of the active site in conjunction with sequence alignments to homologous methyltransferases and phylogenetic analysis strongly suggest PsiM evolved from monomethylating RNA methyltransferases. Mutagenesis studies support our evolutionary hypothesis through the production of PsiM mutants that mimic ancestral activity through the inability to produce psilocybin. Ultimately, our findings suggest PsiM is not an ideal methyltransferase for biotechnological production of psilocybin analogs due to the delicate nature of substrate binding resulting from its evolutionary history.
  • Publication
    Seismic imaging by nonlinear inversion
    (Colorado School of Mines. Arthur Lakes Library, 2024) Silva, Werter Oliveira; Sava, Paul C.; Li, Yaoguo; Jin, Ge
    Imaging aims to create representations of internal object structures through indirect external physical measurements. In seismic exploration, for instance, seismic reflections on the Earth’s surface are mapped into discontinuities in physical properties, revealing geological structures. Various seismic imaging techniques exist, differing in their approach to wave propagation (acoustic or elastic; isotropic or anisotropic), wave equation type (one-way or all-way), application domain (post-stack or pre-stack), numerical implementation (frequency or time domain; integral or differential forms), and other factors. Migrations usually assume a linear relationship between data and image based on the Born approximation, and the image consists of a scalar parameter that describes the spatial distribution of subsurface reflectors. Since seismic data includes not only primary reflections but also multiples that do not satisfy the Born approximation, imaging is normally preceded by multiple attenuation to meet the linear assumption and avoid creating fake reflectors and crosstalk noise. However, multiples provide additional illumination and resolution because they can sample subsurface image points at angles different from those of the primary waves. Therefore, multiple attenuation ignores additional information that could be used to improve the image. In this thesis, I introduce an acoustic nonlinear inversion imaging method, based on a parameterization of the wave equation that preserves the nonlinearity between data and image, defined as a vector instead of a scalar function. This parameterization separates propagation and dynamic effects. Wave propagation is ruled by a background velocity model, lacking sharp contrasts, while the dynamics of reflections is controlled by the image vector parameter I seek to invert. The vectorial nature of the image reflects the directional dependence of the reflectivity and its nonlinear dependence to the data enables multiple-scattering modeling to fit unprocessed data, containing multiples and ghots in addition to primaries.
  • Publication
    Synthesis and applications of organophosphonic acid compounds as extractants for rare earth element separation and beyond
    (Colorado School of Mines. Arthur Lakes Library, 2024) Kuvayskaya, Anastasia; Sellinger, Alan; Jensen, Mark; Domaille, Dylan; Wu, Ning
    The realization of a shift from traditional energy sources towards more environmentally friendly alternatives has led to an ever-growing need for essential raw materials such as rare earth elements (REEs). Nuclear energy, catalysis, phosphors, superconductors, permanent magnets, and optical materials rely heavily on REEs. Consequently, a crucial area of technology is the extraction and isolation of REEs from complex mixtures. Chemical homogeneity causes various REEs to accumulate in source minerals, making it more challenging for their separation and obtaining commercially feasible pure elements requires multistage extractions and repeated separation techniques. Solvent extraction is a commercially employed technique for separating rare earth metals. Extractants are crucial to the separation process because they can form complexes with the water-soluble REE cations and switch their solubility into the organic phase. Many extractants have been developed, including carboxylic and phosphorous acids, β-diketones, phosphorous esters, phosphine oxides, and various amines. Commercial extractants, however, have low selectivity, which renders processing time-, energy-, and solvent-intensive. Recently, promising REE separation results have been reported on organophosphorus extractants, including asymmetric dialkylphosphinic acids, monoalkylphosphinic acids, and styryl phosphonate monoesters. In this work, two generations of aryl vinyl phosphonic acid esters were designed and synthesized. The synthesis optimization resulted in a two-step reaction allowing various high-purity aromatic vinyl phosphonic acid monoesters. Utilization of the Heck coupling reaction enabled functionalization of vinyl phosphonic acid with different aromatic and photoswitchable moieties. The employment of Steglich esterification led to the formation of two generations of organic soluble non-symmetric mono-esters. The 1st generation of extractants was complexed with Eu3+ and studied compared to traditional extractants, resulting in an unexpected finding: the order of increasing extraction strength matched the order of decreasing calculated dipole moment of the synthesized ligands rather than pKa. The 2nd generation of extractants included phosphonic acid esters containing photoswitchable moieties that are currently being studied for their extraction properties. In another application, the employment of a versatile Heck coupling approach resulted in synthesizing 14 diverse anionic monomers capable of modular “cyanostar”-stabilized anion dimerization. The optimized synthetic approach to vinyl phosphonic acids and corresponding vinyl phosphonates allowed access to solubility-tuned ditopic monomers for preparing supramolecular polymers. Finally, the broad scope of applicability of aryl vinyl phosphonic acids was evident from the evaluation of carbazole-based PA derivatives as self-assembled monolayer (SAM)-based hole transport/extraction layers (HTM) in perovskite solar cells. The introduction of stronger bonding molecules at the buried interface reduced the amorphous phase around perovskite/HTM/ITO interfaces and increased the stability of fabricated devices. The champion minimodule with the hybrid HTM retained operational efficiency of 17.5% after 10 weeks of outdoor testing, the first to achieve this property to our knowledge, as independently measured by the Perovskite PV Accelerator for Commercializing Technologies center.
  • Publication
    Phase-field modeling of fracture: regularization length insensitivity and mixed mode ductile fracture
    (Colorado School of Mines. Arthur Lakes Library, 2024) Huber, William; Asle Zaeem, Mohsen; Hedayat, Ahmadreza; Thomas, Brian G.; Tucker, Garritt J.
    Predicting crack nucleation and propagation in materials is of critical importance in designing structural components. Due to the cost, time, and occasional impossibility of performing fracture experiments, computational approaches have become instrumental to understand and assess fracture and failure processes in materials and optimize the design of structures. The development of quantitative computational models for predicting crack initiation and propagation has remained an important area of research because of the complexities that arise from topologically complex crack growth and interactions with other inelastic phenomena. Among computational fracture models, the phase-field modeling approach has emerged as a superior model to overcome the discontinuities associated with cracking. However, we identified a number of shortcomings with existing models, namely in the sensitivity of phase-field model predictions to the regularization length and in the prediction of accurate crack paths and load-displacement curves for ductile materials. In this Ph.D. research, in contrast to previous phase-field fracture models, we proposed a novel approach to attain a length-scale insensitive mechanical response, which considers a continuous approximation of a crack boundary with a function of infinite support. The predicted mechanical response and crack paths were validated against experimental results from a three-point bending test on concrete and an in-plane shear test on steel. These models are capable of predicting crack propagation in a wide range of materials and structures. Additionally, for the first time, we developed a mixed-mode phase-field model for ductile fracture which combines two phase-fields for shear (mode II) and tensile (mode I) fractures. Unlike many previous phase-field models, the proposed model implicitly includes the important effects of lode angle (via the maximum shear stress) and triaxiality (via the first principal stress and pressure) on the initiation and propagation of ductile fracture. Model predictions of slant and cup cone crack paths as well as load-displacement responses were comparable to the results of plane-strain tension, round bar tension and notched round bar tension experiments in Al 2024-T351. The proposed model is a practical tool for ductile fracture prediction in a wide range of stress states. Finally, the developed phase-field models were applied to the study of mode II crack propagation in a heterogeneous domain consisting of intermetallic particles inside an aluminum alloy matrix (Al 2024). Attention was given to the effects of particle size and area fraction on predicted crack growth resistance curves. In this Ph.D. research, we introduced advanced phase-field models for the accurate prediction of complex crack paths and mechanical responses in engineering materials under a variety of loading configurations. These models are practical tools to predict, understand and assess fracture and failure processes in a variety of materials.
  • Publication
    Opportunities for use of quantum spin glasses as reservoir in time series prediction
    (Colorado School of Mines. Arthur Lakes Library, 2024) Shiekh, Kylee N.; Kapit, Eliot; Wu, Bo; Wu Fung, Samy
    This thesis investigates the paradigm of Quantum Reservoir Computing (QRC), a cutting-edge framework that employs fixed quantum circuits to improve neural network performance. Rooted in the principles of Reservoir Computing, this model of QRC diverges by integrating a quantum reservoir capable of adapting to multivariable time series data without recurrent circuit modifications between training sessions. Reservoir Computing, a subset of machine learning, centers on harnessing dynamic systems, or reservoirs, to process information and simplify computations. Within this framework, the quantum reservoir exhibits intrinsic adaptability to complex data structures, enabling seamless encoding of intricate temporal relationships within multivariable datasets. Furthermore, this research contextualizes Quantum Computing, a revolutionary field leveraging quantum mechanics principles to revolutionize computation. Quantum phenomena, such as superposition and entanglement, underpin the principles of quantum computing. The current state of quantum computing explores harnessing these phenomena to develop powerful computational frameworks, yet remains in a nascent stage due to challenges in achieving and maintaining quantum coherence and scalability. This study showcases the potential efficacy of the proposed QRC model in multivariable time series prediction, demonstrating its capability in handling intricate dependencies within complex datasets. By integrating the quantum spin glass model as the quantum reservoir, this research underscores the adaptability of such reservoirs in encoding temporal relationships and capturing intricate data dynamics. This work accentuates the advantages of Quantum Reservoir Computing over conventional quantum machine learning frameworks, which rely on backpropogation and gradient descent, with more efficient use of computational resources. This work contributes to the evolving landscape of Quantum Reservoir Computing, shedding light on successful implementations while delineating avenues for refinement. By exploring successful applications and contextualizing within the evolving field of quantum computing, this thesis guides future directions for the refinement and expansion of quantum computing frameworks, specifically in the realm of multivariable time series data processing.
  • Publication
    Forecasting the timeline for quantum advantage and economic viability using option pricing
    (Colorado School of Mines. Arthur Lakes Library, 2024) Carau, Frank Paul, Jr.; Kapit, Eliot; Lange, Ian; Mehta, Dinesh P.
    The potential for quantum computing to significantly reduce the time necessary to process and analyze data has attracted the attention of major financial institutions. These companies are continually researching ways to accelerate data processing and analysis to react faster to market changes and improve the results of their decisions. Quantum computing holds promise as a “game changer” for several different financial applications such as modeling, risk analysis, portfolio planning and automated trading. However, it is unclear if and/or when a quantum computing advantage will exist over current methods and computers. Estimates for such an advantage range anywhere from 3 to 20+ years in the future. The purpose of this project is to provide guidance on when quantum computing will be economically viable for the finance industry. To focus the research, a specific type of finance application: option pricing, was chosen for analysis. Based on this research, an economically viable quantum computer for option pricing will not be available until 2037 at the earliest, with a more likely timeframe of 2040. Further, the payoff period for investment could take another 3 to 5 years. This paper covers available data for predicted improvements in quantum computing hardware, and improvements in algorithms for option pricing, to forecast when such a computer will be available.
  • Publication
    Optimal control and speed limits of two-qubit quantum gates
    (Colorado School of Mines. Arthur Lakes Library, 2024) Basyildiz, Bora; Gong, Zhe-Xuan; Simmonds, Raymond; Kapit, Eliot
    The speed of elementary quantum gates, especially two-qubit gates, sets a fundamental limit on how fast a quantum computer can run. For current quantum computers that are subject to noise and errors, the speed of quantum gates is even more important as qubits have finite coherence times, and faster quantum gates directly lead to a larger circuit depth. This is crucial in solving real-world problems. For a simple system made of just two qubits, the speed limit of a given two-qubit gate is proportional to the interaction strength between the two qubits, and this can be found exactly, if arbitrarily fast single qubit gates are allowed. The knowledge of such speed limits allows one to design gate protocols that are speed optimized. However, for more complicated scenarios, the exact speed limit of two-qubit gates is generally unknown. In this thesis, we study the speed limits of two-qubit gates for a system of two interacting qudits. In many quantum computing platforms, there exist extra physical states outside the qubit subspace that can be well controlled, and these states may enable faster implementations of two-qubit gate without increasing the physical interaction strength of the two qubits. However, the exact speedup for this is not known. Thus in this work we derive a rigorous upper bound for this speedup, and we further show that for experimentally relevant systems we can saturate this bound exactly, showing that a time optimal gate protocol exists in the absence of noise and off-resonant transitions. For a practical experiment, we need to consider the off-resonant transitions due to the strong but finite-strength single-qudit drives. We again develop and use quantum optimal control software to generate optimized drive pulses that achieve high-fidelity target two-qubit gates using two qutrits close to their theoretical speed limits. We expect our results to be testable in near-term experiments with parametrically coupled transmons.
  • Publication
    Influence of cooling rate on microstructure and properties in low-temperature tempered medium-carbon low-alloy martensitic steels
    (Colorado School of Mines. Arthur Lakes Library, 2024) Rupinen, Michael Christopher, Jr.; Speer, J. G.; Clarke, Amy; Findley, Kip Owen; De Moor, Emmanuel; Gockel, Joy
    The use of steels requiring thick section sizes (greater than 12.5 cm) with high strength (>1200 MPa) and impact toughness (>35 J at room temperature) maintained throughout the component has raised new questions regarding the effect of alloying additions and cooling rate on properties. Large section sizes may lead to significant differences in cooling rate throughout the component during processing causing both hardenability and autotempering to be of relevance. The effect of autotempering (tempering of the martensite during quenching) is thought to be of particular importance as these steels are typically tempered at or below 204 °C while the martensite start temperatures may be well over 350 °C. The goal of this study was to investigate the effects of alloying additions and cooling rate on the impact toughness and strength of two sets of medium-carbon low alloy steels following a 204 °C temper. The first set of three alloys referred to as the “Base” alloys had systematic variations in Mo and V content. The results of the Base alloy study showed that hardenability was the key factor in determining toughness as the least-hardenable steel often had upper bainite present that led to a significant decrease in the upper shelf impact energy. Differences in toughness between fully martensitic conditions of the three alloys were small and were attributed to differences in the prior austenite grain size, carbon content, and strength between the alloys. The second set of alloys included two AF9628 steels with 0.25 and 1 wt pct Si respectively. These highly hardenable steels were used to determine the effects of cooling rate (i.e. autotempering) and Si on low temperature tempering response and on microstructural evolution during cooling. Additionally, a general Hollomon-Jaffe based tempering parameter model was developed to quantify the degree of autotempering experienced by every incremental fraction of martensite formed during quenching and to directly compare autotempering effects to isothermal tempering effects. The experimental results using the AF96 steels showed agreement between tempering parameter and hardness for autotempered conditions validating this approach. Specimens of the AF96 alloys were also quenched in various media to produce different degrees of autotempering. Tensile and Charpy testing along with Mossbauer effect spectroscopy, transmission electron microscopy and high-energy X-ray diffraction were used to determine effects of Si and cooling rate. The results showed significant decreases in impact toughness and yield strength with decreased cooling rate in fully martensitic, low temperature tempered conditions for both alloys. The decreased yield strength and impact energy with slower cooling were attributed to the changes in retained austenite. Slower cooling rates led to increased retained austenite fractions in both alloys (leading to decreased YS through yielding at low strains), but the slower cooling rate specimens also showed increased decomposition of retained austenite following tempering at 204 °C. It is therefore believed that the decomposition of retained austenite during tempering (seen only in slower cooled specimens) is the mechanism responsible for the lower impact toughness in slow-cooled specimens. Significant differences in the fine-scale microstructure were observed between the two AF9628 alloys due to the effects of Si. Increased Si content was shown to inhibit carbide formation during autotempering, increase the fraction of retained austenite during slow cooling, and inhibit carbide formation during low temperature tempering. Comparing the mechanical properties of the two alloys, similar strengths were measured for both, but the low Si variant had significantly reduced toughness which was attributed to the increased carbide fractions and possibly increased cementite precipitation.
  • Publication
    Carbon capture, utilization, and storage (CCUS) potential for the Niobrara A and B intervals at Redtail field, Weld County, Colorado
    (Colorado School of Mines. Arthur Lakes Library, 2024) Beliveau, Chris; Sonnenberg, Stephen A.; Carr, Mary; Kazemi, Hossein; Majewski, Dave
    Carbon capture, utilization, and storage (CCUS) is the process of capturing carbon dioxide (CO2), injecting it into reservoirs to enhance oil and gas production, and safely and permanently storing it in the subsurface. This process has become more common in the oil and gas industry both as a technology to enhance production, and for companies to work towards carbon neutrality. While carbon capture, and storage (CCS) has sometimes garnered more attention, carbon capture, utilization, and storage (CCUS) is more attractive as it offers the additional economic incentive of increased hydrocarbon production as primary and secondary oil and gas recovery methods can still leave up to ~80% of oil in the reservoir. CCUS is used for enhanced oil recovery and can be a more effective technology for recovering additional hydrocarbons with the added benefit of safely sequestering CO2 in the subsurface. CCUS is continuing to expand and has the potential to capture ~6GtCO2 per year by 2050. The Niobrara System was deposited in the Western Interior Cretaceous Seaway (WICS) during the Late Cretaceous by a series of sea level transgressions and regressions. Carbonate deposition in the WICS was controlled by cooler, oxygen-rich water from the north, mixing with warmer, oxygen-poor water from the south. In the Denver-Julesburg Basin, the carbonate-rich Niobrara A and B chalk beds exhibit favorable petrophysical properties for hydrocarbon production with increased resistivity and porosity. Consequently, they have both been extensively produced in recent years, and it is important to evaluate this reservoir as a potential CCUS target. Core data from the Razor 25-2514H well in Redtail Field was evaluated to determine if the Niobrara A and B could be a viable CCUS target. Porosity and permeability measurements combined with production flow and injection treatments of CO2 acting on the core plugs to replicate primary and EOR production were used to determine if the reservoir properties in the Niobrara A and B are favorable for CCUS. Results from the Redtail Field study area can then be applied to other fields in the Denver-Julesburg Basin leading to increased hydrocarbon recovery and the safe storage of CO2.
  • Publication
    Towards understanding deformation mechanisms in 3D layered solids under compression
    (Colorado School of Mines. Arthur Lakes Library, 2024) Zhao, Xingyuan; Lamberson, Leslie; Berger, John R.; Barsoum, M. W.; Gockel, Joy; Reimanis, Ivar E. (Ivar Edmund)
    This thesis explores the unique rate-dependent behavior and applications of 3D layered materials known for their anisotropic properties. Specifically, MAX phases are distinguished by their kink band formation, a distinct deformation mechanism in layered materials. These materials effectively bridge the properties of metals and ceramics, offering a balance of strength and toughness. This combination of attributes positions MAX phases as promising candidates for advanced applications, such as in high-efficiency engine components and nuclear cladding systems, which demand resilience against both static and dynamic loading environments. The research focuses on the compressive behavior of MAX phases, particularly highly oriented Ti$_3$SiC$_2$ polycrystalline samples prepared through hot forging.~The influence of global grain orientation along the c-axis, strain rate, composition, and stress state on the compressive response is explored experimentally.~A~Kolsky (or split-Hopkinson) bar is utilized to assess the dynamic compressive response under uniaxial, biaxial (planar confinement), and triaxial (radial confinement) conditions.~Additionally, a modified nonlinear buckling theory is developed to analytically examine kinking deformation behavior at the continuum scale. Observations from macroscopic ultra-high-speed visualization during loading and microscopic post-mortem fractography indicate that confinement states significantly affect both macroscopic failure patterns and microscopic fracture mechanisms.~Notably, biaxial loading with dynamic load edge-on to the grains and 80~MPa planar confinement parallel to the c-axis resulted in the highest dynamic compressive strength observed (1636$\pm$136~MPa), a 66\% increase compared to the unconfined uniaxial condition.~This planar confinement appears to delay crack propagation and enhance inelastic deformation. Radial confinement at 70~MPa showed potential for inelastic deformation and ductile fracture surfaces, a first for MAX phases, though it was less conducive to kink band formation.~These findings underscore the critical competition between brittle and pseudo-ductile deformation mechanisms enhancing compressive strength and broaden our understanding of how to tailor the use of next-generation layered materials for specific applications.
  • Publication
    Empowering special education teachers: exploring challenges and opportunities with socially-assistive robots
    (Colorado School of Mines. Arthur Lakes Library, 2024) Romero, Shane; Williams, Thomas; Thompson, Rob H.; Reddy, Elizabeth
    This thesis addresses the critical intersection of socially assistive robots (SARs) and special education, with a primary focus on the role of teleoperators— special educators—in shaping the effective implementation of SARs. The three interconnected studies provide a comprehensive perspective on the essential aspects of SAR utilization in special education. In Study One, session summary and progress reports emerged as multifaceted tools integral to the credibility of SAR interventions. Balancing visualization for a diverse audience while ensuring teleoperators have adequate details for informed judgments, such as engagement and proficiency metrics, proves crucial. Study Two delves into the nuanced needs of special education teachers, revealing the intricate landscape of the field. The challenge lies in designing for diverse tracking methods and multifaceted dimensions of success, including academic goals, behavioral observations, social interactions, and health metrics. This complexity necessitates careful consideration of collaborative dynamics, presenting a challenge in creating a universally effective design. Study Three highlights the significance of a structured support system, emphasizing community building among special educators. Practical strategies, including continuous assistance, hands-on sessions, accessible resources, and incentivized professional development, empower educators and enhance their understanding of SARs. The study underscores the specific needs of special educators, providing valuable considerations for institutions to support effective implementation. In conclusion, this collectively emphasize the dual importance of refining teleoperation interfaces and ensuring effective implementation to ensure SAR success in special education. Technological advancements alone are insufficient; the key lies in strategies empowering and supporting educators operating SARs. This research advocates for a holistic approach, focusing on the perspectives of special educators. Such an approach ensures widespread SAR adoption and positive impacts on the lives of children in special education settings.
  • Publication
    Integrating core lithofacies and rock properties to inform mechanical stratigraphy: Wolfcamp XY, central Delaware Basin, Texas
    (Colorado School of Mines. Arthur Lakes Library, 2024) Jaramillo, Israel; Wood, Lesli J.; Jobe, Zane R.; Melick, Jesse
    This research used a core in the Delaware Basin, where hydraulic stimulation is standard. Hydraulic stimulation fractures a rock; thus, understanding the data type and how data resolution impacts the characterization of geomechanics, and brittleness is essential. Typically, elastic properties from wireline logs define brittleness where fine-scale brittleness heterogeneity is poorly resolved. This research examines the impact of three data resolution scales on brittleness curves created using core-collected rebound hardness (0.5 ft), X-ray fluorescence (0.4 inches), and wireline log data (0.5 ft). The brittleness curves from the rebound hardness data and X-ray fluorescence data better resolved large-scale brittle versus ductile interfaces, which were almost indistinguishable in the brittleness curve derived from the wireline logs. Seven lithofacies were described and analyzed across the core at 2 feet per inch, tracking sedimentological variability, which is linked to geomechanical properties (Young’s modulus, closure stress, and rock strength). To show that the mechanical properties of lithofacies are unique enough to use as inputs for models, the lithofacies geomechanical properties and brittleness uniqueness was quantified using a pairplot. This work adds to the understanding of clay content characterization by highlighting that some research has stated that low UCS is preferable to hydraulic stimulation (typically found in high clay content rocks); however, in the Wolfcamp XY, low UCS is disadvantageous since it is indicative of low brittleness, low Young’s modulus, higher clay content, and higher closure stress on average. This work has applications in geocellular modeling and the energy industries, where a better understanding of the mechanical quality of rock helps with well placement.
  • Publication
    Geology, alteration, and mineralization of the La Virgen high-sulfidation epithermal - porphyry district, northern Peru
    (Colorado School of Mines. Arthur Lakes Library, 2024) Montesinos, Raul; Chang, Zhaoshan; Enders, M. Stephen; Holley, Elizabeth A.
    This study seeks to fill a knowledge gap, enrich our understanding of high-sulfidation (HS) ore-forming processes in siliciclastic environments, and guide exploration in siliciclastic terranes, by studying the La Virgen district in northern Peru, 17 km east of the giant Lagunas Norte HS deposit, in which the HS mineralization is mostly hosted in the sandstone of the Chimu Formation and other siliciclastic rocks. In addition, this study is the first detailed study of the La Virgen District and discovered the porphyry style mineralization in the eastern part of the district, and that the eastern part of the district has mineralization significantly older than the western part based on mapping, geochronology, SWIR (Short Wavelength Infra-Red) spectral analysis, and whole rock geochemistry. The sedimentary rocks of the La Virgen District are Low Cretaceous siliciclastic rocks with minor limestones that are folded at least twice and chopped up by many faults of various timing. The faults had multiple movements; some of them generated tectonic breccia that were later on altered and cemented by hydrothermal fluids, changing the breccias to tectonic-hydrothermal breccias. The sedimentary rocks were intruded by andesite porphyry, feldspar porphyry, and phreatomagmatic breccias of ~22-21 Ma, and later dacite porphyries and their related phreatomagmatic breccias of ~17 Ma. The alteration and mineralization occurred in two events and two domains: ~22-21 Ma porphyry-HS mineralization in the Escalerilla-Cuypampa Domain in the east, with the source being the feldspar porphyry in its Cuypampa block, and the ~18-17 Ma HS mineralization in the La Virgen Domain, with its magmatic center possibly below Cerro Alumbre. There are five types advanced argillic alteration (AA1: vuggy quartz + pyrite ± alunite; AA2: quartz + alunite + pyrite; AA3: dickite + pyrite ± alunite; AA4: kaolinite + pyrite ± illite; and AA5: quartz + pyrite + pyrophyllite.), intermediate argillic alterations (IA: illite and/or smectite + pyrite, and chlorite + smectite ± pyrite) in the HS deposits, and K-feldspar alteration and slightly later phyllic alteration (quartz-sericite-pyrite) associated with the porphyry-style mineralization. The alteration is structurally and lithology-controlled. The AA and IA alterations are typically zoned. The highly fractured and brecciated sandstone of the Chimu Formation are altered by AA alterations in which alunite, dickite, pyrophyllite, and quartz fill the interstitial open spaces between the resistant quartz grains, fill microfractures, and replace minor feldspar grains. The alteration is cryptic, with the altered sandstone appearing fresh. The alteration minerals also cement and alter clasts of tectonic-hydrothermal breccias. The Cu-Au HS mineralization consists of pyrite, enargite, and minor famatinite, luzonite, covellite, digenite, sphalerite, galena, tennantite, tetrahedrite, and visible gold. Gold also occurs in pyrite2, pyrite3, and enargite, as revealed by LA-ICP-MS mapping. HS mineralization is accompanied by silicification that occurs partly as black silica with fine-grained pyrite and partly as creamy silica. The silicification also fills interstitial open spaces between grains of the sandstone, fractures in sandstones, and as cement of breccias. The porphyry style mineralization consists of pyrite, molybdenite and chalcopyrite. The lesson for HS exploration in siliciclastic terranes is that SWIR analysis should be widely applied to identify cryptic clay minerals in reconnaissance exploration, even if the rocks look fresh.
  • Publication
    Effects of thermomechanical pretreatment on abnormal grain growth during simulated carburization, The
    (Colorado School of Mines. Arthur Lakes Library, 2024) Gruich, James M.; Findley, Kip Owen; De Moor, Emmanuel; Cryderman, Robert
    Carburization followed by quenching, and tempering is frequently utilized in the automotive industry to increase the surface hardness and compressive residual stress of a steel alloy while retaining toughness and ductility in the core. At carburizing temperatures, austenite grains are formed and abnormal grain growth (AGG) can occur. During AGG, the steel microstructure undergoes bimodal grain growth with some grains growing exponentially faster than others. The growth of large austenite grains through AGG compromises the fatigue performance of carburized steels. AGG has been shown to be further exacerbated by cold work introduced into the alloy prior to carburizing. Warm and cold work are also sometimes utilized in part forming prior to carburizing. In this study, the effects of warm work and warm work in combination with cold work on austenite grain size were investigated. AISI 4121with added Al and N and a modified AISI 4121 with additions of Nb and Mo were homogenized, warm reduced by 0-50 pct at a temperature of 900 ℃, subjected to cold reduction ranging from 0-25 pct, and then heated in a furnace for 0 328 min at a temperature of 930 ℃ after ramping up 8 ℃ min-1 from room temperature to simulate a carburizing heat treatment without a carburizing atmosphere. WR resulted in refinement of the resulting ferritic and secondary microconstituent microstructures. The average prior austenite grain size (PAGS) and AGG also tended to decrease as WR and CR increased. The refinement due to WR and CR were roughly equivalent, but the addition of CR tended to decrease the effectiveness of grain refinement due to WR. The alloy condition with the coarsest average PAGS and highest degree of AGG was 4121Nb after a 328 min hold time, equivalent to a full carburization cycle. 4121Al had a higher relative grain refinement across a majority of experimental conditions, as well as a lower degree of AGG on average. The precipitates present in 4121Al were exclusively AlN and those present in 4121Nb included both AlN and finer precipitates interpreted to be Nb(C,N).
  • Publication
    Development of catalase like nanomaterials for tandem systems in the industrial synthesis of keto acids
    (Colorado School of Mines. Arthur Lakes Library, 2024) Berstler, Calvin Andrew; Trewyn, Brian; Domaille, Dylan; Vyas, Shubham
    The pursuit of novel strategies for conducting multi-step chemoenzymatic catalysis within a single reaction vessel remains a challenging undertaking. A chemoenzymatic process represents a distinct category of reactions wherein two or more consecutive transformations take place in a single reaction vessel, and subsequent post-reaction processing is minimized. This process leverages both enzymatic and chemical catalysis to efficiently generate desired products from commercially available starting materials, while removing the need to isolate intermediates. Driven by emerging techniques for designing biosynthetic materials that employ enzymes and inorganic species within single-pot systems, innovative use of catalytically active mesoporous nanomaterials as enzyme supports has potential to significantly enhance the overall performance and capabilities of the combined catalysts. In this work, we investigate material properties that influence the catalytic activity of metal phosphate materials. Specifically, we focus on further understanding the structure-function relationship of these materials which have catalase-like activity by synthesizing bulk and mesoporous cobalt phosphate materials with varying levels of crystallinity and surface areas. Catalases, which are known for their proficiency in decomposing hydrogen peroxide in biological systems, are used in a wide range of applications such as in medicine, catalysis, and environmental remediation. Our research demonstrates the impact of synthesis and aging temperatures on morphology and material properties of cobalt phosphate materials, as well as the resulting catalytic activity bringing structure-function relationships together. Furthermore, we explore the potential of employing mesoporous cobalt phosphate with enlarged pores and increased surface area as catalysts and stabilizing agents in a chemoenzymatic system to efficiently synthesize keto acids. By encapsulating and covalently immobilizing enzymes such as L-amino acid oxidase or L-glutamate oxidase within the pores of cobalt phosphate materials, we aim to develop a more efficient and recyclable hybrid tandem system that effectively bridges bio- and chemo-catalysis.
  • Publication
    Barriers and strategies to achieve an equitable transition to residential building electrification: a case study of Los Angeles
    (Colorado School of Mines. Arthur Lakes Library, 2024) Sandoval, Noah T.; Landis, Amy E.; Harris, Chioke; Tabares-Velasco, Paulo Cesar; Bazilian, Morgan; Gilbert, Benjamin
    Widespread residential building electrification is a key component of achieving federal, state, and local decarbonization mandates. While there has been significant research into technologies needed to achieve residential building electrification, existing research has not investigated technology deployment, and more specifically, equitable deployment in a timely manner to mitigate the worst impacts of climate change. In this dissertation, an energy justice-informed study design is used to explore viable pathways to achieve residential buildings electrification and outline the possible consequences of these pathways to ensure no household is over-burdened or left behind in this transition. First, a comparative framework is developed to analyze the scenario development process of energy models and is then applied to the development of high-quality electrification scenarios for the residential building sector. Second, a high-resolution techno-economic model is developed to calculate all costs associated with electrification upgrades. Setting a variable discount rate for each household based on income, this model compares the upgrades of varying efficiency levels for all the major electrification end uses – space heating, water heating, cooking, and clothes drying – and reports results based on income, building type, renter/owner status, and household cooling use. Lastly, two electrification supportive strategies – improved building envelope characteristics and universal access to cooling using heat pumps – are evaluated to determine if there are any synergistic benefits with the previously evaluated electrification upgrades. The work of this dissertation improves the scenario development and economic analysis of residential building electrification and provides a novel study design that incorporates the tenets of energy justice.