Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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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 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 Kinetics of thermally inactivated ureases and management of sand production through ureolysis-induced mineral precipitation(Montana State University - Bozeman, College of Engineering, 2018) Morasko, Vincent John; Chairperson, Graduate Committee: Robin Gerlach; Adrienne Phillips (co-chair)Biocement has the potential to seal subsurface hydraulic fractures, manipulate subsurface flow paths to enhance oil recovery, treat fractured cement, stabilize soil structures and minimize dust dispersal. Biocement can be formed using the urease enzyme from various sources (bacteria, plant, or fungi) to break down urea into carbonate, combining with calcium for use in engineering applications such as biocement production. Higher temperatures, pressures, and extreme pH conditions may be encountered as these engineering applications expand deeper into the subsurface. Temperatures beyond 1000 meters can exceed 80°C, potentially rapidly inactivating the enzyme. The first part of this study focused on monitoring urea hydrolysis catalyzed by jack bean urease at temperatures ranging from 20-80°C. An increasing rate of urease inactivation was observed with increasing temperatures and first-order models described the kinetics of urea hydrolysis and enzyme inactivation properly. The second part of this study focused on developing a technology to mitigate sand transport in oil and gas wells. This study addressed a method to cement sand in the subsurface so that it is not returned when oil or gas is extracted. As the sand leaves the formation, it can cause damage in the subsurface, leading to economic concerns, as well as reducing the lifespan of pumps, piping and other components on the well pad. A reactor system was developed to mimic a subsurface oil well that produces sand. Biocement production was promoted within the reactor, utilizing common sources of urease (Sporosarcina pasteurii and Canavalia ensiformis or jack bean meal). The resultant calcium carbonate/sand mass was subjected to elevated flowrates, simulating field conditions where sand is potentially fluidized and potentially transported into the wellbore. It was shown that biocement can reduce sand transport while allowing for higher flow rates than conditions without biocement. The findings from this study broaden the potential application range of biocementation technologies into higher temperature environments. Applying biocement specifically to sand mitigation may have significant environmental, economic, and safety implications within the natural resource industry.