Theses and Dissertations at Montana State University (MSU)
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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 Characterization of the effects of hygrothermal-aging on mechanical performance and damage progression of fiberglass epoxy composite(Montana State University - Bozeman, College of Engineering, 2018) Voth, Michael Mark; Chairperson, Graduate Committee: David A. MillerMarine Hydro-Kinetic Devices (MHK) are a developing renewable energy technology that allows energy to be harvested from the natural flow of water due to tides, currents, and waves. Fiber Reinforced Polymers (FRP), which have been extensively used in wind energy applications, offer favorable mechanical properties as well as low costs and manufacturability making them a viable option for construction of MHK devices. However, exposure to a harsh marine environment results in moisture uptake into the FRP, often degrading mechanical properties. A study of a fiberglass-epoxy FRP was conducted to characterize the effects of moisture on mechanical properties and damage behavior of the material as well as classify the degradation mechanisms responsible for changes in performance. Environmental exposure was simulated through hygrothermal aging, exposing the FRP samples to distilled water and elevated temperature (50 °C) to accelerate the environmental effects. Quasi-static tension tests of both unidirectional and cross-ply laminates were conducted to classify the effects of moisture on mechanical properties of constituent and multi-angle laminates. Cross-ply laminates experienced 54% reduction in strengths due to moisture absorption, while unidirectional laminates strengths were reduced by 40%. Constitutive stress-strain response in conjunction with Acoustic Emission (AE) monitoring describe changes in damage behavior due to hygrothermal aging. This work also characterizes hygrothermal effects on pure/neat epoxy material to aid in interpreting hygrothermal degradation mechanisms in the composite as well as guided ultrasonic evaluation of composite specimens to characterize effects of moisture on AE signals.Item Stabilization of metallic catalyst microstructures against high-temperature thermal coarsening(Montana State University - Bozeman, College of Engineering, 2016) Driscoll, David Robert; Chairperson, Graduate Committee: Stephen W. Sofie; Clay D. Hunt, Julie E. Muretta and Stephen W. Sofie were co-authors of the article, 'Thermally stabilized nickel electro-catalyst introduced by infiltration for high temprature electrochemical energy conversion' in the journal 'Transactions of the Electrochemical Society' which is contained within this thesis.; Cameron H. Law and Stephen W. Sofie were co-authors of the article, 'Design and synthesis of metallic nanoparticle-ceramic support interfaces for enhancing thermal stability' in the journal 'Ceramic transactions' which is contained within this thesis.; Stephen W. Sofie was a co-author of the article, 'Stabilization of nano-scale metallic microstructure against thermal coarsening' in the journal 'Ceramic transactions' which is contained within this thesis.; Melissa D. McIntyre, Martha M. Welander, Stephen W. Sofie and Robert A. Walker were co-authors of the article, 'Enhancement of high temperature metallic catalysts : aluminum titanate in the nickel-zirconia system' in the journal 'Applied catalysis A: general' which is contained within this thesis.; Thesis contains two articles of which David Robert Driscoll is not the main author.; Melissa D. McIntyre, Martha M. Welander, Daniel E. Perea, Robert A. Walker and Stephen W. Sofie were co-authors of the article, 'Aluminum oxide processed as a beneficial additive in SOFC anodes' submitted to the journal 'Journal of the electrochemical society' which is contained within this thesis.; Clay D. Hunt, Daniel E. Perea, and Stephen W. Sofie were co-authors of the article, 'Diffusion caging : thermodynamic arrest of Ostwald ripening' submitted to the journal 'Advanced Materials' which is contained within this thesis.The size and shape of metal particulate at high temperature is dictated by surface energy. In systems containing very small metal particles, smaller particles shrink and disappear as they grow into larger particles in a process referred to as coarsening. Coarsening causes irreversible degradation in a number of important systems including automotive catalytic converters and solid oxide fuel cells (SOFC) through a loss of catalyst (metal) surface area. This phenomenon is exemplified by nickel metal catalyst that is supported on ytrria-stabilized zirconia (YSZ) which represents a materials system critical to the function of SOFCs. It has been demonstrated that additions of aluminum titanate (ALT) to the Ni-YSZ system with subsequent thermal treatment can act to stabilize the geometry of Ni on YSZ. In demonstration SOFCs, ALT has increased the time required for the first 10% of degradation by a factor of 115. This work has sought to elucidate the mechanisms by which ALT imparts increased stability. The work contained here demonstrates that ALT easily decomposes to Al 2O 3 and TiO 2. During thermal treatment, the alumina reacts with NiO to form nickel aluminate and the titania interacts with the YSZ where it can form Zr 5Ti 7O 24 -- a mixed ion electron conducting phase. In this way, the Al and Ti components of ALT have been determined to act independently where alumina appears to be dominant in microstructural stabilization. During cell operation, the nickel aluminate decomposes to nickel metal decorated with alumina nano-particulate. This geometry forms the basis of 'diffusion caging' as a stabilization mechanism which is the subject of Chapter 8. The role of titania appears to be less important except when processing occurs in a way that facilitates formation of the MIEC phase. However, Ni-YSZ cermets have also shown a strength enhancement when doped with ALT. This strength enhancement is likely due to the influence of titania (Chapter 7). Future work has the potential to extend concepts discussed here to a number of high temperature catalytic systems.Item High temperature chlorosilane corrosion of iron and AISI 316L stainless steel(Montana State University - Bozeman, College of Engineering, 2016) Aller, Joshua Loren; Chairperson, Graduate Committee: Paul E. GannonChlorosilane gas streams are used at high temperatures (>500°C) throughout the semiconductor, polycrystalline silicon, and fumed silica industries, primarily as a way to refine, deposit, and produce silicon and silicon containing materials. The presence of both chlorine and silicon in chlorosilane species creates unique corrosion environments due to the ability of many metals to form both metal-chlorides and metal-silicides, and it is further complicated by the fact that many metal-chlorides are volatile at high-temperatures while metal-silicides are generally stable. To withstand the uniquely corrosive environments, expensive alloys are often utilized, which increases the cost of final products. This work focuses on the corrosion behavior of iron, the primary component of low-cost alloys, and AISI 316L, a common low-cost stainless steel, in environments representative of industrial processes. The experiments were conducted using a customized high temperature chlorosilane corrosion system that exposed samples to an atmospheric pressure, high temperature, chlorosilane environment with variable input amounts of hydrogen, silicon tetrachloride, and hydrogen chloride plus the option of embedding samples in silicon during the exposure. Pre and post exposure sample analysis including scanning electron microscopy, x-ray diffraction, energy dispersive x-ray spectroscopy, and gravimetric analysis showed the surface corrosion products varied depending on the time, temperature, and environment that the samples were exposed to. Most commonly, a volatile chloride product formed first, followed by a stratified metal silicide layer. The chlorine and silicon activities in the corrosion environment were changed independently and were found to significantly alter the corrosion behavior; a phenomenon supported by computational thermodynamic equilibrium simulations. It was found that in comparable environments, the stainless steel corroded significantly less than the pure iron. This is likely due to the alloying elements present in stainless steel that promote formation of other stable silicides. Mechanistic models were developed to describe the formation and evolution of metal silicide and/or metal chloride surface corrosion products in chlorosilane environments. These models will help inform materials selection and/or support process development for next-generation chlorosilane-based production and deposition systems. The implementation of low cost materials of construction in these systems could lower the cost of final products in these industries.Item Investigation of multivalent double perovskites as electrodes for high temperature energy conversion(Montana State University - Bozeman, College of Engineering, 2012) Weisenstein, Adam John; Chairperson, Graduate Committee: Stephen W. Sofie; Nick Childs, Roberta Amendola, David Driscoll, Stephen Sofie, Paul Gannon and Richard Smith were co-authors of the article, 'Processing and characterization of Sr 2-xVMoO 6-delta double perovskites' submitted to the journal 'Journal of materials chemistry and physics' which is contained within this thesis.; Stephen Sofie was a co-author of the article, 'Fuel electrode performance of Sr 2VMoO 6 double perovskites' which is contained within this thesis.Solid Oxide Fuel Cells (SOFCs) are direct energy conversion devices that have demonstrated viability due to the associated high efficiencies, utilization of transition metal catalyst, and their unique fuel flexibility, which allows the use of dirty hydrocarbons. These high temperature systems typically utilize fuel electrodes composed of a ceramic/metal (cermet) composite that is comprised of nickel and yittria-stabilized zirconia (YSZ). While these systems have demonstrated performance potential due to the catalysis and electrical conductivity of nickel metal, a key shortcoming is the poor thermal stability of nickel metal at operating temperatures of 750-1000°C, for which increased temperature enhances performance. Nickel metal particle networks as well as other transition metal catalysts operating at high temperatures coarsen or agglomerate resulting in the loss of continuous electronic pathways. To address these challenges, new materials have been sought after to replace the mixed metal and ceramic two-phase Ni/YSZ fuel electrode. One proposed solution is to utilize a single phase Mixed Ionic Electronic Conductor (MIEC) to replace the traditional cermet structure. In this study, the analysis and characterization of the processing and sintering of Sr 2-xVMoO 6-delta perovskites, where x=0.0, 0.1 and 0.2, was investigated. Sr 2-xVMoO 6-delta substrates were sintered in a reducing atmosphere (5%H 2 95%N 2) and the x-ray diffraction patterns indicate that the double perovskite is the primary phase for Sr 2-xVMoO 6-delta pellets sintered at 1200°C and 1300°C for 20 hours. However, these pellets show a secondary phase of SrMoO 4-delta. X-ray photoelectron spectroscopy revealed a deficiency of vanadium on the pellet surfaces in which samples yielded surface vanadium concentrations of less than 5%. The vanadium inhomogeneity can be explained by the formation of the SrMoO 4-delta scheelite phase due to oxygen exposure on the surface of the pellets, which indicates inward vanadium migration to the bulk. Sr 2-xVMoO 6-delta pellets sintered at 1300°C showed very high conductivity, with Sr 1.9VMoO 6-delta exhibiting conductivity over 100,000S/cm at room temperature. The conductivity tests also indicate a semiconductor to metallic transition for all double perovskites related to the reduction of Mo6+ to Mo4+. Utilizing the double perovskites as fuel electrodes proved to be difficult, due to anion transport leading to secondary phases and thus delamination.