Theses and Dissertations at Montana State University (MSU)
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Item Condensation of chromium vapor, generated in high-temperature (>800°C) environments, and interactions with aluminosilicate surfaces(Montana State University - Bozeman, College of Engineering, 2024) van Leeuwen, Travis Kent; Chairperson, Graduate Committee: Paul E. Gannon; This is a manuscript style paper that includes co-authored chapters.This work represents a collection of research and reporting with the goal of improving fundamental understanding of chromium (Cr) vapor reactive condensation, relevant in many high-temperature (>800°C) process environments where Cr-containing alloys are used. While reactive evaporation of Cr from stainless steels used in high-temperature solid oxide electrochemical systems is well-documented, the dynamics of Cr condensation onto surrounding interfaces during complex and dynamic system operation is less understood. Understanding these interactions during operation is critical for improving system performance and safeguarding environmental, health and safety, as some condensed species contain hexavalent chromium (Cr(VI)), a known carcinogen. A series of studies were designed and conducted to investigate the condensation pathways of Cr vapors within representative high-temperature system environments, simulating extreme conditions for Cr evaporation and downstream aluminosilicate fibers used in high-temperature insulation. The first study focuses on the influence of water vapor concentration in the gaseous environment on reactive Cr condensation and speciation onto aluminosilicate fibers. The second study explores the effects of alkaline oxide additives in aluminosilicate fibers on Cr condensation and speciation. The third study investigates the effects of presence of alkaline oxides within the Cr vapor source on reactive evaporation and condensation of Cr vapors onto downstream aluminosilicate fibers. To accomplish the specific objectives of these studies, Cr vapors, produced by high-temperature (>800°C) air exposures of trivalent chromium (Cr(III)) oxide (Cr 2O 3) (chromia) powder with variable moisture content, were condensed onto various ceramic materials (aluminosilicate fibers) downstream at lower temperatures (100-500°C). Total condensed Cr and ratios of oxidation states were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES) and diphenyl carbazide (DPC) colorimetric/direct UV-VIS spectrophotometric analyses, respectively. Results indicate presence of both Cr(III) and Cr(VI) species condensed on all samples investigated. Total Cr and ratio of Cr(VI) to total Cr detected was significantly more on those containing alkaline oxides and at higher atmospheric water vapor concentration, while the presence of alkaline oxides in the Cr vapor source (Cr 2O 3) decreased the evaporation and amount of Cr/Cr(VI) condensed on the samples downstream. Computational thermodynamic equilibrium modelling helps explain experimental results showing the relative stability of alkaline-chromate compounds.Item Forming properties of stretch broken carbon fiber for aircraft structures(Montana State University - Bozeman, College of Engineering, 2023) Nold, Dalton Bradley; Chairperson, Graduate Committee: Dilpreet S. Bajwa; Douglas S. Cairns (co-chair); This is a manuscript style paper that includes co-authored chapters.Continuous carbon fiber is known to be a superior material for its strength, stiffness, and high strength-to-weight ratio and is often incorporated in aerospace composites. A challenge, however, is that it's not versatile in forming deep drawn geometries, which require convoluted manufacturing techniques resulting in expensive components. To overcome this, a type of carbon fiber with a random discontinuous fiber alignment called stretch broken carbon fiber (SBCF) is proposed. SBCF has potential to form parts with complex geometries with comparable or better mechanical properties to that of continuous carbon fiber. Montana State University (MSU) developed its own version of SBCF manufacturing processes, and research is being conducted to understand how SBCF prepreg tows react to stretch drawing at elevated temperatures using aerospace-grade epoxy resin systems. Currently, several new methods have been proposed to rapidly test these materials. This research revealed that SBCF forms with greater ease than continuous carbon fiber and is expected to substantially reduce manufacturing times for aircraft structures. To comprehend the material's behavior, simple tensile tests were coursed to understand how gauge length and temperature affected the peak loads when compared to continuous carbon fiber. It was discovered that on average, SBCF experienced stresses that were ten times less than continuous fibers. Additional tensile tests were conducted at elevated temperature to determine the true stress versus true strain. These tests are particularly important because they represent the material's most accurate mechanical properties. The results led to the discovery that SBCF experienced strain softening behavior. Furthermore, a series of forming tests using a novel "forming fixture" revealed that increasing the gap lowered the peak forming loads while the plunger geometry had little to no effect on peak forces at both room and elevated temperatures.Item Thermoregulatory adaptations of the wetsalts tiger beetle, Cicindelidia haemorrhagica, in Yellowstone National Park(Montana State University - Bozeman, College of Agriculture, 2021) Bowley, John Lawrence; Chairperson, Graduate Committee: Robert K. D. Peterson; This is a manuscript style paper that includes co-authored chapters.The wetsalts tiger beetle, Cicindelidia haemorrhagica (LeConte) is found throughout Yellowstone National Park (YNP) associated with active thermal hot spring areas with surface temperatures that exceed 50 °C. Previous studies suggest that YNP C. haemorrhagica behaviorally thermoregulate differently than populations from Idaho not associated with hot springs. However, the cause of this behavioral difference is unknown. Therefore, our study had five objectives: 1) compare internal temperatures of YNP and Idaho adult C. haemorrhagica in similar environmental conditions; 2) determine if the cuticular wax influences YNP beetle internal body temperature; 3) measure and analyze venter reflectivity of YNP and Idaho beetles; 4) compare YNP and Idaho beetle abdominal structures using scanning electron microscopy; and 5) analyze thermal video recordings of YNP adults to estimate times spent on different surface temperatures. Internal temperatures of freshly killed adults were recorded using thermocouples inserted into the abdomen and were suspended over a heated water bath. Our results found a mean difference of 1.03 °C between YNP and Idaho beetle internal temperatures, suggesting that the exoskeleton reflects more heat in YNP adults. Our results suggest that the wax does not play a significant role in temperature reduction. The dissected exoskeletal ventral abdominal face experienced a mean difference of 0.58 °C compared to an imitation venter, suggesting the venter was primarily responsible for heat reflection. Spectrophotometric differences revealed greater reflective properties of YNP beetle venters. Scanning electron microscopic images indicated no visible structural differences between YNP and Idaho beetles. Thermal video analysis indicated YNP adults spent an increasing amount of time on surface temperatures greater than 20 °C, but decreasing amounts of time on surfaces temperatures greater than 40 °C. Beetles from only one YNP location were on surfaces exceeding 50 °C. Our results suggest that physical properties of the abdominal venter of YNP beetles are likely responsible for improved heat reflection from bottom-up heating of hot spring areas. Improved heat reflection resulted in lower internal temperatures of YNP beetles relative to Idaho.Item Temperature dependent second harmonic generation studies of materials used in energy conversion applications(Montana State University - Bozeman, College of Engineering, 2022) McNally, Marshall Traver; Chairperson, Graduate Committee: Robert Walker; This is a manuscript style paper that includes co-authored chapters.Materials in energy conversion devices often undergo a variety of degradation mechanisms. Solid oxide fuel cell cathodes materials, for example, are subject to surface compositional changes due to material segregation. The extreme operating conditions in these energy conversion devices requires the development of an operando technique that is surface and material specific to accurately probe these degradation mechanisms. Second harmonic generation (SHG) is a surface specific technique that probes the electronic structure of a material using the 2nd order polarizability. Using well characterized materials like Au, Si and NiO, we began investigating how high temperatures (260 °C) and atmospheric composition affected the surface electronic structures. To do this, a custom sample chamber dubbed TROPICS was designed and built to achieve temperature, atmospheric compositional and eventually, electrochemical control. We found that gold's SH intensity was enhanced (3.5 times) when O 2 was present in the atmosphere but this enhancement disappeared at high temperatures. Using data from titrating O 2 into a N 2 atmosphere, we concluded that a monolayer of O 2 was forming on the gold surface, providing backbonding opportunities for gold's free electrons into the partially filled O 2 pi* orbitals. Similar behavior was seen in N-type Si which also showed SH enhancement at room temperature. However, P-type and undoped Si showed no such atmospheric dependent behavior. SHG experiments done with NiO showed decoupled behavior in the electronic structure recovery between the bulk and surface. After heating to 260 °C, the SH signal did not return to pre-heating intensities but required ~60 and ~90 minutes in N 2 and air respectively. The difference in recovery time between N 2 and air could be attributed to interactions between the still paramagnetic NiO electrons and the partially filled O 2 pi* orbitals.Item The effects of atomic oxygen on silicon-carbon systems in extreme environments(Montana State University - Bozeman, College of Letters & Science, 2021) Chen, David Zuyu; Chairperson, Graduate Committee: Timothy Minton; Chenbiao Xu, Vanessa J. Murray and Timothy K. Minton were co-authors of the article, 'Oxidation of silicon carbide through the passive-to-active transition' submitted to the journal 'The journal of chemical physics' which is contained within this dissertation.; Chenbiao Xu and Timothy K. Minton were co-authors of the article, 'Effect of atomic oxygen on CV-1144-0 and RTV-560 silicones' submitted to the journal 'Acta astronautica' which is contained within this dissertation.; Chenbiao Xu and Timothy K. Minton were co-authors of the article, 'Effect of silicone coating on atomic oxygen reactivity with fiberform and phenolic impregnated carbon ablator' submitted to the journal 'Journal of spacecraft and rockets' which is contained within this dissertation.Vehicles traveling at hypersonic speeds require thermal protection systems (TPSs) that can withstand the extreme temperatures and reactive atomic oxygen species present in these environments. Ultra-high temperature ceramics are candidate TPSs, and many of them contain silicon carbide, allowing them to resist chemical attack by forming a protective oxide-containing layer, called passive oxidation. At very high temperatures, however, the layer will decompose, subjecting the material to ablation from reaction with O-atoms, called active oxidation, through a process called the passive-to-active oxidation transition (PAT). We have conducted molecular beam-surface scattering experiments to investigate the interactions of O-atoms with SiC at high temperatures, which revealed that with a lower fluence of O-atoms above the PAT, the SiC surface undergoes graphitization, while a sufficiently higher fluence of O-atoms promotes active oxidation. Analysis of the oxide layer decomposition revealed a decomposition process that initiated at the oxide-SiC interface. These insights will be useful for the development of more accurate predictive models, but they also aided understanding of the ablation of silicone-coated heat shields for atmospheric entry applications. For these applications, phenolic impregnated carbon ablator (PICA), a material composed of a carbon fiber network (FiberForm) and a resole phenolic resin stable against high heat convection and conduction, is used. Silicone is sprayed onto PICA to reduce dust, but the silicone can also form an oxide layer, which, like on SiC, will resist O-atom attack until it decomposes at very high temperatures, exposing the underlying material to reactive O-atoms. We conducted additional experiments in which a beam of atomic oxygen was directed at silicone-coated and uncoated samples of PICA as well as FiberForm, which revealed high nonreactive O-atom product scattering when the oxide layer was present, while with the decomposition of the oxide, product scattering resembled O-atom scattering from the underlying substrate. Additional studies probed the oxidation layer that is formed on pure silicone during O-atom bombardment, which revealed a three orders of magnitude reduction in erosion yield compared to that of Kapton H, a polyimide. This new data on PICA and FiberForm has been provided to NASA Ames for their development of an ablation model.Item Operando optical studies of next generation anode materials in high temperature solid oxide fuel cells(Montana State University - Bozeman, College of Letters & Science, 2020) Welander, Martha Maria; Chairperson, Graduate Committee: Robert Walker; Marley S. Zachariasen, Clay D. Hunt, Stephen W. Sofie and Robert A. Walker were co-authors of the article, 'Operando studies of redox resiliance in alt enhanced NIO-YSZ SOFC anodes' in the journal 'Journal of the electrochemical society' which is contained within this dissertation.; Marley S. Zachariasen, Stephen W. Sofie and Robert A. Walker were co-authors of the article, 'Enhancing Ni-YSZ anode resilience to environmental redox stress with aluminum titanate secondary phases' in the journal 'ACS applied energy materials' which is contained within this dissertation.; Marley S. Zachariasen, Stephen W. Sofie and Robert A. Walker were co-authors of the article, 'Mitigating carbon formation with Al 2TiO 5 enhanced solid oxide fuel cell anodes' in the journal 'The journal of physical chemistry C' which is contained within this dissertation.; Daniel B. Drasbaek, Marie L. Traulsem Bhaskar R. Sudireddy, Peter Holtappels and Robert A. Walker were co-authors of the article, 'What does carbon tolerant really mean? Operando vibrational studies of carbon accumulation on novel solid ocide fuel cell anodes prepared by infiltration' submitted to the journal 'RSC physical chemistry chemical physics' which is contained within this dissertation.; Disseration contains an article of which Martha Maria Welander is not the main author.Solid oxide fuel cells (SOFCs) are high temperature energy conversion devices capable of efficient and sustainable energy production. Because of the need to electrochemically reduce molecular oxygen and the relatively high activation energy required for oxide ions to diffuse through the dense, solid-state electrolyte, SOFCs typically operate at temperatures > or = 500 °C. High operating temperatures endow SOFCs with many advantages, including fuel flexibility and high conversion efficiencies, distinguishing them from other types of fuel cells. However, high temperatures also present challenges related to the stability of the electrode materials, accelerating cell degradation and limiting the development and integration of SOFCs into large scale power production strategies. These mechanisms are the result of fundamental changes in material properties that remain poorly described and difficult to predict. Studies presented in this work utilized operando Raman spectroscopy and electrochemical measurements to directly correlate material changes with changes in cell performance under various operating conditions. Research focused on developing and characterizing new electro-catalytic materials having improved conversion efficiencies and mechanical resilience to thermal and chemical stress. Because current state of the art SOFC Ni-YSZ cermet anodes are sensitive to oxidation, the first two studies investigated the effects of adding small amounts of Al 2TiO 5 to Ni-YSZ anodes and the impact of resulting secondary (2°) phases that formed on SOFC tolerance to electrochemical and environmental reduction and oxidation (redox) cycling. Results show that Al 2TiO 5 helps improve tolerance to both types of redox cycling by maintaining electrode-electrolyte connectivity and minimizing catalyst coarsening. The third study illustrates how this same dopant improved anode carbon tolerance when operating with hydrocarbon fuels. Because excessive carbon accumulation on SOFC anodes can lead to rapid cell failure, ways to improve carbon tolerance was further explored in the last two studies. These studies investigate the effect of decoupling the electro-catalytic and the electronically conductive phases of the anode under pure methane and biogas-surrogate environments. Collectively, the studies described in this dissertation provide insight into the materials-specific mechanisms responsible for limiting degradation of doped and functionally decoupled anodes to help guide the design of new SOFC electrode materials.