Current Search: solid (x)
Pages
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Title
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Mechanochemical Synthesis of Fuels from Sustainable Sources Utilizing Solid Catalysts.
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Creator
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Todd, Jacob, Zhai, Lei, Blair, Richard, Hampton, Michael, Harper, James, Rahman, Talat, University of Central Florida
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Abstract / Description
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The transition to biofuels as a means of curbing the emissions of greenhouse gases has given rise to several questions such as what to use as the feedstock and how to cost effectively process them.(&)nbsp; The production of bio-derived chemicals presents challenges in synthesis and in use as a drop-in fuel replacement.(&)nbsp; Through the use of mechanochemistry reaction pathways can be utilized that allow the efficient production of biofuels and bioderived chemicals.(&)nbsp; To this end...
Show moreThe transition to biofuels as a means of curbing the emissions of greenhouse gases has given rise to several questions such as what to use as the feedstock and how to cost effectively process them.(&)nbsp; The production of bio-derived chemicals presents challenges in synthesis and in use as a drop-in fuel replacement.(&)nbsp; Through the use of mechanochemistry reaction pathways can be utilized that allow the efficient production of biofuels and bioderived chemicals.(&)nbsp; To this end mechanically driven esterification and transesterification reactions were studied.(&)nbsp; It was found that the acid base properties of solid catalysts was critical to efficient reactions.(&)nbsp; Further investigation into mechanocatalytic reaction resulted in a reaction scheme where glucose can be used as a feedstock for the production of propane from glucose through a retro aldol reaction followed by hydrodeoxygenation.(&)nbsp; The use of mechanochemistry facilitates the efficient synthesis of important energy molecules and allows new reaction pathways to be exploited.(&)nbsp; The efficient production of bio-derived chemicals will reduce our impact on the environment.(&)nbsp;(&)nbsp;
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Date Issued
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2017
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Identifier
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CFE0006809, ucf:51805
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006809
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Title
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HIGH PRESSURE TESTING OF COMPOSITE SOLID ROCKET PROPELLANT MIXTURES: BURNER FACILITY CHARACTERIZATION.
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Creator
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Carro, Rodolphe, Petersen, Eric, University of Central Florida
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Abstract / Description
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Much Research on composite solid propellants has been performed over the past few decades and much progress has been made, yet many of the fundamental processes are still unknown, and the development of new propellants remains highly empirical. Ways to enhance the performance of solid propellants for rocket and other applications continue to be explored experimentally, including the effects of various additives and the impact of fuel and oxidizer particle sizes on burning behavior. One...
Show moreMuch Research on composite solid propellants has been performed over the past few decades and much progress has been made, yet many of the fundamental processes are still unknown, and the development of new propellants remains highly empirical. Ways to enhance the performance of solid propellants for rocket and other applications continue to be explored experimentally, including the effects of various additives and the impact of fuel and oxidizer particle sizes on burning behavior. One established method to measure the burning rate of composite propellant mixtures in a controlled laboratory setting is to use a constant-volume pressure vessel, or strand burner. To provide high-pressure burn rate data at pressures up to 360 atm, the authors have installed, characterized and improved a strand burner facility at the University of Central Florida. Details on the facility and its improvements, the measurement procedures, and the data reduction and interpretation are presented. Two common HTPB/AP propellant mixtures were tested in the original strand burner. The resulting burn rates were compared to data from the literature with good agreement, thus validating the facility and related test techniques, the data acquisition, data reduction and interpretation. After more than 380 successful recordings, an upgraded version of the strand burner, was added to the facility. The details of Strand Burner II, its improvements over Strand Burner I, and its characterization study are presented.
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Date Issued
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2007
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Identifier
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CFE0001979, ucf:47427
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001979
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Title
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Structure of reflectin protein probed by solid-state nuclear magnetic resonance.
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Creator
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Boykin, Tommy, Chen, Bo, Schulte, Alfons, Tatulian, Suren, Teter, Kenneth, University of Central Florida
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Abstract / Description
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An unusual protein found in squids, termed reflectin, possesses the unique ability for optical reflectivity and proton conductivity. Reflectin has the potential to become optically and electronically tunable, however, the molecular structure of reflectin has yet to be determined. Previous literature has considered using reflectin proteins as diffraction gratings, protonic transistors, and substrates for neural stem cell growth. Applying recombinant protein techniques, we purified the...
Show moreAn unusual protein found in squids, termed reflectin, possesses the unique ability for optical reflectivity and proton conductivity. Reflectin has the potential to become optically and electronically tunable, however, the molecular structure of reflectin has yet to be determined. Previous literature has considered using reflectin proteins as diffraction gratings, protonic transistors, and substrates for neural stem cell growth. Applying recombinant protein techniques, we purified the reflectin 4Ax4 protein. We determined the leucine, tryptophan, and threonine amino acids are in an ordered state by solid-state nuclear magnetic resonance (NMR). Knowing these ordered amino acids is possibly the key to understanding reflectin's natural optical and electrical properties. Understanding the link between reflectin's structure and electrical properties is essential to make the next generation of bioelectronic materials based on inexpensive, natural resources.
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Date Issued
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2019
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Identifier
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CFE0007433, ucf:52712
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0007433
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Title
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Fate of Coated Zinc Oxide in Municipal Solid Waste Landfills.
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Creator
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Bolyard, Stephanie, Reinhart, Debra, Santra, Swadeshmukul, Randall, Andrew, University of Central Florida
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Abstract / Description
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Given the increase in nanomaterial (NM) use in consumer products and the large fraction of waste placed in landfills worldwide, the probability of these products reaching municipal solid waste (MSW) landfills at the end of their useful life is high. Since nanotechnology use is still in its early stages, there are currently no regulations pertaining to the disposal of NMs and their fate in MSW landfills is still unknown. Understanding the fate of NMs in MSW landfills is vital to ensure the...
Show moreGiven the increase in nanomaterial (NM) use in consumer products and the large fraction of waste placed in landfills worldwide, the probability of these products reaching municipal solid waste (MSW) landfills at the end of their useful life is high. Since nanotechnology use is still in its early stages, there are currently no regulations pertaining to the disposal of NMs and their fate in MSW landfills is still unknown. Understanding the fate of NMs in MSW landfills is vital to ensure the proper handling of these novel materials from cradle to grave; such research will provide information on how these NMs can be safely introduced into the environment. This research seeks to understand the fate of NMs within waste environments by examining the interactions between NMs and landfill leachate components. The primary focus of this thesis is the effect of Zinc Oxide (ZnO) on biological landfill processes, solids aggregation, and chemical speciation of Zn in landfill leachate following the addition of crystalline, nano-sized ZnO coated with triethoxycaprylylsilane. This research (1) observed the effects of coated ZnO on five-day biochemical oxygen demand (BOD5) and biochemical methane potential (BMP), (2) examined effects of solids aggregation on the fate of ZnO, (3) quantified the concentration of Zinc (Zn) by size fractions, and (4) modeled the chemical speciation of Zn in landfill leachate using Visual MINTEQ.No change in dissolved Zn was observed after coated ZnO was exposed to (")middle-aged(") leachate. Upon exposure to (")mature(") leachate there was an increase in dissolved Zn assumed to be a result of the dissociation of ZnO. Solids data supported the aggregation of particles in both middle aged and mature leachate. There was an increase in the Zn concentration in leachate fractions greater than 1500 nm presumably due to the dispersion of normally insoluble ZnO nanoparticles (NPs) following the interaction with humic acids (HA). ZnO did not inhibit anaerobic or aerobic processes in either middle aged or mature leachate, presumably due to the relatively low concentration of dissolved ionic Zn. Despite the observation of increased dissociation upon exposure to mature leachate, the presence of dissolved organic matter (DOM) may have hindered the ability for dissolved ionic Zn to become bioavailable. Fractionation, BOD5 and BMP tests, and chemical speciation modeling provided insight on the mobility of ZnO in landfills and the absence of inhibitory effects on landfill processes. Aggregation of ZnO NPs may prevent movement through traditional containment systems (i.e. geomembrane liners) due to the increased particle size. However, the increased dispersion suggests that ZnO NPs will be transported out of the landfill in the leachate, however biological treatment of leachate should be unaffected by the presence of ZnO. The bioavailability of Zn was not substantially affected by the presence of ZnO due to affinity of dissolved Zn for DOM. However, due to the heterogeneity of landfill leachate and the utilization of different NM coatings, it is challenging to predict the overall mobility of other NMs in a landfill.
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Date Issued
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2012
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Identifier
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CFE0004264, ucf:49509
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004264
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Title
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Novel Nanostructures and Processes for Enhanced Catalysis of Composite Solid Propellants.
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Creator
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Draper, Robert, Seal, Sudipta, Heinrich, Helge, Zhai, Lei, University of Central Florida
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Abstract / Description
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The purpose of this study is to examine the burning behaviour of composite solid propellants (CSP)in the presence of nanoscale, heterogenous catalysts. The study targets the decomposition of am-monium perchlorate (AP) as a key component in the burning profile of these propellants, and seeksto identify parameters of AP decomposition reaction that can be affected by catalytic additives.The decomposition behavior of AP was studied in the presence of titanium dioxide nanoparticlesin varying...
Show moreThe purpose of this study is to examine the burning behaviour of composite solid propellants (CSP)in the presence of nanoscale, heterogenous catalysts. The study targets the decomposition of am-monium perchlorate (AP) as a key component in the burning profile of these propellants, and seeksto identify parameters of AP decomposition reaction that can be affected by catalytic additives.The decomposition behavior of AP was studied in the presence of titanium dioxide nanoparticlesin varying configurations, surface conditions, dopants, morphology, and synthesis parameters withthe AP crystals. The catalytic nanoparticles were found to enhance the decomposition rate of theammonium perchlorate, and promote an accelerated burning rate of CSP propellants containingthe additives. Furthermore, different configurations were shown to have varying degrees of effec-tiveness in promoting the decomposition behaviour.To study the effect of the catalyst's configuration in the bulk propellant, controlled dispersion con-ditions of the nanoparticle catalysts were created and studied using differential scanning calorime-try, as well as model propellant strand burning. The catalysts were shown to promote the greatestenthalpy of reaction, as well as the highest burn rate, when the AP crystals were recrystalizedaround the nanoparticle additives. This is in contrast to the lowest enthalpy condition, which cor-responded to catalysts being dispersed upon the AP crystal surface using bio-molecule templates.Additionally, a method of facile, visible light nanoparticle tracking was developed to study theeffect of mixing and settling parameters on the nano-catalysts. To accomplish this, the titaniananoparticles were doped with fluorescent europium molecules to track the dispersion of the cat-alysts in the propellant binder. This method was shown to succesfully allow for dispersion andagglomeration monitoring without affecting the catalytic effect of the TiO2 nanoparticles.
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Date Issued
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2013
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Identifier
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CFE0004991, ucf:49559
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004991
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Title
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Comparative Histology of the Respiratory Tract of Normal Persmyscus Floridanus and P. Gossypinus and Effects of Exposure to Solid Rocket Motor Fuel Exhaust on P. Gossypinus.
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Creator
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Bitner, Terry L., Stout, I. Jack, Natural Sciences
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Abstract / Description
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Florida Technological University College of Natural Sciences Thesis; Microscopic examination of the tracheal dimensions of normal Florida mice (Peromyscus floridanus) and cotton mice (P. gossypinus) showed no significant differences between the two species, but external examination showed the tracheal length of the Florida mouse to be longer than that of the cotton mouse. Microscopic examination of the intrapulmonary apparatus (bronchioles, alveolar ducts, atria, and alveoli) of normal...
Show moreFlorida Technological University College of Natural Sciences Thesis; Microscopic examination of the tracheal dimensions of normal Florida mice (Peromyscus floridanus) and cotton mice (P. gossypinus) showed no significant differences between the two species, but external examination showed the tracheal length of the Florida mouse to be longer than that of the cotton mouse. Microscopic examination of the intrapulmonary apparatus (bronchioles, alveolar ducts, atria, and alveoli) of normal Florida and cotton mice showed no significant differences in measurements between the two species. Cotton mice were exposed to exhaust gases produced by the burning of solid rocket motor (SRM) fuel. Mice exposed once for a duration of 10 min demonstrated an LD50 of 52 to 56 ppm HCl/g body weight and an LD50 of 169 to 173 mg Al2O3/m3/g body weight. These LD50 values suggested that SRM exhaust components may have a synergistic lethal effect when compared to the effects of individual components of the exhaust. Cotton mice exposed to the exhaust exhibited external signs of respiratory distress and dyspnea. Those mice that received lethal exposures showed internal signs of early inflammatory reactions. However, the most likely cause of death was a sudden shift in blood pH.
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Date Issued
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1977
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Identifier
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CFR0011601, ucf:53040
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFR0011601
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Title
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Characterization of Waste-To-Energy (WTE) Bottom and Fly Ashes in Cementitious Materials.
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Creator
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An, Jin Woo, Nam, Boo Hyun, Yun, Hae-Bum, Chopra, Manoj, An, Linan, University of Central Florida
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Abstract / Description
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Waste-to-Energy (WTE) ashes (or called as municipal solid waste incineration ashes) have been recycled in the areas of road bed, asphalt paving, and concrete products in many European and Asian countries. In those countries, recycling programs (including required physical properties and environmental criteria) of ash residue management have been developed so as to encourage and enforce the reuse for WTE ashes instead of landfill disposal. However, the U.S. has shown a lack of consistent and...
Show moreWaste-to-Energy (WTE) ashes (or called as municipal solid waste incineration ashes) have been recycled in the areas of road bed, asphalt paving, and concrete products in many European and Asian countries. In those countries, recycling programs (including required physical properties and environmental criteria) of ash residue management have been developed so as to encourage and enforce the reuse for WTE ashes instead of landfill disposal. However, the U.S. has shown a lack of consistent and effective management plans as well as environmental regulations for the use of WTE ashes. Many previous studies demonstrated the potential beneficial use of WTE ash as an engineering material with minimum environmental impacts. Due to persistent uncertainty of engineering properties and inconsistency in the Federal and State regulations in the U.S., the recycling of WTE ash has been hindered, and they are mostly disposed of in landfills. The goal of this study is to identify beneficial use of WTE ashes as construction materials; thus, the recycling program of WTE ashes will become more active in the U.S. One of potential applications for the WTE ashes can be cement-based materials because the ashes contain good chemical components such as calcium and silicon. Moreover, toxics (heavy metals) can be bound or encapsulated in cement matrix; thus, the leaching potential can be reduced. The specific objectives are: (1) to understand the current practice of the reuse of WTE ashes as construction materials, (2) to physically and chemically characterize WTE bottom and fly ashes, (3) to investigate the effects of WTE bottom and fly ashes in cementitious materials (e.g. cement paste and concrete) as replacement of either cement of fine aggregate with emphasis on cement hydration, and (4) to investigate the environmental impacts of WTE bottom ash on leaching when used in cement-based materials. Fundamental properties of MSWI bottom ash and fly ash were studied by conducting physical, microstructural, and chemical tests. Petrographic examinations, such as scanning electron microscopy (SEM), energy dispersive x-ray (EDX), and x-ray diffraction (XRD) were performed in order to identify chemical composition of the ash and to determine their contents. To evaluate the main side effect of ash when used in concrete, the creation of a network of bubbles due to the presence of aluminum, ashes and aluminum powder were submerged in high pH solution, and the evolution of hydrogen gas was measured. Efforts were made to investigate the influence of WTE ashes on engineering properties of cement paste and concrete specimens when part of Portland cement and fine aggregate are replaced with ground and sieved WTE ashes. Cement paste and concrete cylinders were cast with various amounts of mineral and fine aggregate additions, respectively, and their strength and durability were investigated. Subsequently, optimum mix proportioning of the WTE ashes was investigated when they are used in cement paste and concrete specimens. In addition, the leaching characteristics of major alkaline and trace elements from concrete containing varied amounts (10%-50%) of BA were investigated by Synthetic Precipitation Leaching Procedure (SPLP) batch testing.
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Date Issued
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2015
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Identifier
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CFE0006251, ucf:51070
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006251
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Title
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Effects of Allotropic Transformations on Interdiffusion Behavior in Binary Systems.
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Creator
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Ewh, Ashley, Sohn, Yongho, Suryanarayana, Challapalli, Coffey, Kevin, University of Central Florida
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Abstract / Description
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Diffusion plays a significant role in most materials systems by controlling microstructural development. Consequently, the overall properties of a material can be largely dependent upon diffusion. This study investigated the interdiffusion behavior of three binary systems, namely, Mo-Zr, Fe-Mo, and Fe-Zr. The main interest in these particular metals is for application in nuclear fuel assemblies. Nuclear fuel plates generally consist of two main components which are the fuel and the cladding....
Show moreDiffusion plays a significant role in most materials systems by controlling microstructural development. Consequently, the overall properties of a material can be largely dependent upon diffusion. This study investigated the interdiffusion behavior of three binary systems, namely, Mo-Zr, Fe-Mo, and Fe-Zr. The main interest in these particular metals is for application in nuclear fuel assemblies. Nuclear fuel plates generally consist of two main components which are the fuel and the cladding. Due to diffusional interactions that can occur between these two components, a third is sometimes added between the fuel and cladding to serve as a diffusion barrier layer. Fe, Mo, and Zr can act as either cladding or barrier layer constituents and both Mo and Zr also serve as alloying additions in uranium based metallic fuels. Therefore, a fundamental understanding of the diffusional interactions in these systems is critical in predicting the performance and lifetime of these fuels. In order to study this diffusion behavior, a series of solid-to-solid diffusion couples were assembled between Fe, Mo, and Zr. These couples were then diffusion annealed isothermally for various predetermined times over a range of temperatures, including some both above and below the allotropic transformation temperatures for Fe and Zr. Following the diffusion anneal, the couples were water quenched, cross-sectioned, and prepared for microstructural and compositional characterization. A combination of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron probe microanalysis (EPMA) were used to obtain micrographs showing the microstructure and to collect compositional data for identifying intermediate phases and determining concentration profiles across the interdiffusion zone.Based on this characterization, the phases that developed in the diffusion zones were identified. In the Mo-Zr system, a large Zr solid solution layer developed in the couples annealed at and above 850(&)deg;C and a thin (~1-2 ?m) layer of Mo2Zr formed in all couples. Growth constants and concentration dependent interdiffusion coefficients were calculated for the Mo2Zr and Zr solid solution phases, respectively. In the Fe-Mo system, both the ?-Fe2Mo and ?-Fe7Mo6 phases were observed in couples annealed at 900(&)deg;C and below while ?-Fe7Mo6 and ?-Fe solid solution layers were observed in couples annealed above 900(&)deg;C. The relevant growth constants and activation energies for growth were calculated. In the Fe-Zr system, the couple annealed at 750(&)deg;C developed an FeZr2 and an FeZr3 layer while the couple annealed at 850(&)deg;C developed an Fe2Zr and Fe23Zr6 layer in the diffusion zone. The results of this analysis were then compared to available information from literature and the corresponding binary phase diagrams for each system. The results are discussed with respect to the effects of the allotropic transformations of Fe and Zr on the interdiffusion behavior in these systems.
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Date Issued
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2012
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Identifier
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CFE0004374, ucf:49422
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004374
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Title
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MULTICOMPONENT INTERDIFFUSION IN AUSTENITIC NI-, FE-NI-BASE ALLOYS AND L12-NI3AL INTERMETALLIC FOR HIGH-TEMPERATURE APPLICATIONS.
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Creator
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Garimella, Narayana, Sohn, Yong-ho, University of Central Florida
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Abstract / Description
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Interdiffusion in multicomponent-multiphase alloys is commonly encountered in many materials systems. The developments of multicomponent-multiphase alloys require control of microstructure through appropriate heat treatment, involving solid-state transformations, precipitation processes, and surface modification, where the interdiffusion processes play a major role. In addition, interdiffusion processes often control degradation and failure of these materials systems. Enhanced performance and...
Show moreInterdiffusion in multicomponent-multiphase alloys is commonly encountered in many materials systems. The developments of multicomponent-multiphase alloys require control of microstructure through appropriate heat treatment, involving solid-state transformations, precipitation processes, and surface modification, where the interdiffusion processes play a major role. In addition, interdiffusion processes often control degradation and failure of these materials systems. Enhanced performance and reliable durability always requires a detailed understanding of interdiffusion. In this study, ternary and quaternary interdiffusion in Ni-Cr-X (X = Al, Si, Ge, Pd) at 900C and 700C, Fe-Ni-Cr-X (X = Si, Ge) at 900C, and Ni3Al alloyed with Ir, Ta and Re at 1200C were examined using solid-to-solid diffusion couples. Interdiffusion fluxes of individual components were calculated directly from experimental concentration profiles determined by electron probe microanalysis. Moments of interdiffusion fluxes were examined to calculate main and cross interdiffusion coefficients averaged over selected composition ranges from single diffusion couple experiments. Consistency in the magnitude and sign of ternary and quaternary interdiffusion coefficient were verified with interdiffusion coefficients determined by Boltzmann-Matano analysis that requires multiple diffusion couples with intersecting compositions. Effects of alloying additions, Al, Si, Ge and Pd, on the interdiffusion in Ni-Cr-X and Fe-Ni-Cr-X alloys were examined with respect to Cr2O3-forming ability at high temperature. Effects of Ir, Ta and Re additions on interdiffusion in Ni3Al were examined with respect to phase stability and site-preference. In addition, a numerically refined approach to determine average ternary interdiffusion coefficients were developed. Concentrations and moments of interdiffusion fluxes are employed to generate multiple combinations of multicomponent interdiffusion coefficient as a function of moments. The matrix of multicomponent interdiffusion coefficients corresponds to the lowest order of the moment. It yields real and positive eigen values which provides reliable average interdiffusion coefficients for the selected composition range.
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Date Issued
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2009
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Identifier
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CFE0002521, ucf:47639
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002521
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Title
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DESIGN AND IMPLEMENTATION OF AN EMISSION SPECTROSCOPY DIAGNOSTIC IN A HIGH-PRESSURE STRAND BURNER FOR THE STUDY OF SOLID PROPELLANT COMBUSTION.
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Creator
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Arvanetes, Jason, Petersen, Eric, University of Central Florida
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Abstract / Description
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The application of emission spectroscopy to monitor combustion products of solid rocket propellant combustion can potentially yield valuable data about reactions occurring within the volatile environment of a strand burner. This information can be applied in the solid rocket propellant industry. The current study details the implementation of a compact spectrometer and fiber optic cable to investigate the visible emission generated from three variations of solid propellants. The grating was...
Show moreThe application of emission spectroscopy to monitor combustion products of solid rocket propellant combustion can potentially yield valuable data about reactions occurring within the volatile environment of a strand burner. This information can be applied in the solid rocket propellant industry. The current study details the implementation of a compact spectrometer and fiber optic cable to investigate the visible emission generated from three variations of solid propellants. The grating was blazed for a wavelength range from 200 to 800 nm, and the spectrometer system provides time resolutions on the order of 1 millisecond. One propellant formula contained a fine aluminum powder, acting as a fuel, mixed with ammonium perchlorate (AP), an oxidizer. The powders were held together with Hydroxyl-Terminated-Polybutadiene (HTPB), a hydrocarbon polymer that is solidified using a curative after all components are homogeneously mixed. The other two propellants did not contain aluminum, but rather relied on the HTPB as a fuel source. The propellants without aluminum differed in that one contained a bimodal mix of AP. Utilizing smaller particle sizes within solid propellants yields greater surface area contact between oxidizer and fuel, which ultimately promotes faster burning. Each propellant was combusted in a controlled, non-reactive environment at a range of pressures between 250 and 2000 psi. The data allow for accurate burning rate calculations as well as an opportunity to analyze the combustion region through the emission spectroscopy diagnostic. It is shown that the new diagnostic identifies the differences between the aluminized and non-aluminized propellants through the appearance of aluminum oxide emission bands. Anomalies during a burn are also verified through the optical emission spectral data collected.
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Date Issued
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2006
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Identifier
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CFE0000971, ucf:46694
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000971
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Title
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PRODUCTION, CONTROL AND ACTUATION OF MICRON-SIZED PARTICLES IN AMICROFLUIDIC T-JUNCTION.
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Creator
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Wilson, James, Kumar, Ranganathan, University of Central Florida
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Abstract / Description
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This research is directed towards understanding the mechanisms associated with the manufacture of solid microspheres less than 100 [micro]m, from liquid droplets with nanosuspensions in a microfluidic T-junction, which are heated downstream of the channel. Preliminary material characterization tests on colloidal suspensions of alumina and copper oxide demonstrate promising temperature dependent viscosity results indicating solidification in the temperature range of 40degC-50degC. The...
Show moreThis research is directed towards understanding the mechanisms associated with the manufacture of solid microspheres less than 100 [micro]m, from liquid droplets with nanosuspensions in a microfluidic T-junction, which are heated downstream of the channel. Preliminary material characterization tests on colloidal suspensions of alumina and copper oxide demonstrate promising temperature dependent viscosity results indicating solidification in the temperature range of 40degC-50degC. The solidification mechanism is referred to as Temperature Induced Forming and is described by polymeric bridges formed between nanoparticles in suspension at elevated temperatures, resulting in a solid structure. The polymer network results from the ionization of alumina at elevated temperatures whereby polymeric binders adhere to newly formed charged sites on the alumina particle. This study aims to investigate the aspects of manufacturing microstructures in microfluidic Tjunctions, droplet morphology, size and frequency of production. Preliminary low solid concentration experiments (1%-10% volume concentration of alumina in H2O) have indicated solidification and a regression in droplet diameter when heated near the saturation temperature of the water used to disperse the particles. The microstructures from this solidification process are uniform and are estimated to be 30 [micro]m in size.
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Date Issued
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2013
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Identifier
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CFH0004387, ucf:44996
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004387
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Title
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MODELING MICROBIOLOGICAL AND CHEMICAL PROCESSES IN MUNICIPAL SOLID WASTE BIOREACTOR: DEVELOPMENT AND APPLICATIONS OF A THREE-PHASE NUMERICAL MODEL BIOKEMOD-3P.
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Creator
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Gawande, Nitin, Reinhart, Debra, University of Central Florida
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Abstract / Description
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The numerical computer models that simulate municipal solid waste (MSW) bioreactor landfills have mainly two components a biodegradation process module and a multi-phase flow module. The biodegradation model describes the chemical and microbiological processes of solid waste biodegradation. The models available to date include predefined solid waste biodegradation reactions and participating species. In a bioreactor landfill several processes, such as anaerobic and aerobic...
Show moreThe numerical computer models that simulate municipal solid waste (MSW) bioreactor landfills have mainly two components a biodegradation process module and a multi-phase flow module. The biodegradation model describes the chemical and microbiological processes of solid waste biodegradation. The models available to date include predefined solid waste biodegradation reactions and participating species. In a bioreactor landfill several processes, such as anaerobic and aerobic biodegradation, nitrogen and sulfate cycling, precipitation and dissolution of metals, and adsorption and gasification of various anthropogenic organic compounds, occur simultaneously. These processes may involve reactions of several species and the available biochemical models for solid waste biodegradation do not provide users with the flexibility to selectively simulate these processes. This research work includes the development of a generalized biochemical process model, BIOKEMOD-3P, which can accommodate a large number of species and process reactions. This model is able to simulate bioreactor landfill processes in a completely mixed condition; when coupled with a multi-phase model it will be able to simulate a full-scale bioreactor landfill. This generalized biochemical model can simulate laboratory and pilot-scale operations which are important to determine biochemical parameters important for simulation of full-scale operations. To illustrate application of BIOKEMOD-3P, two sets of laboratory MSW bioreactors were simulated in this research work. The first demonstrated simulation of data from anaerobic biodegradation of MSW in experimental bioreactors. In another application, simultaneous nitrification and denitrification processes in MSW bioreactors were simulated. The results from these simulations generated information about various modeling parameters that would help implement these processes in a full-scale bioreactor landfill operation.
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Date Issued
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2009
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Identifier
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CFE0002659, ucf:48227
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002659
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Title
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Self-assembly of Rous Sarcoma Virus capsid protein, probed by Solid-state NMR and TEM.
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Creator
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Jeon, Jaekyun, Chen, Bo, Tatulian, Suren, Schulte, Alfons, Cole, Alexander, University of Central Florida
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Abstract / Description
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The retroviral capsid protein (CA) is derived from the cleavage of Gag polyprotein during the maturation process, and self-assembles into a polymorphic fullerene-like shell encasing the viral genome materials. The orthoretroviral CAs, for instance, Human Immunodeficiency Virus (HIV) and Rous Sarcoma Virus (RSV) CA, has little similarity in their sequence composition but a common 3D structure. They form distinct capsid assembly in vivo and a range of similar assemblies in vitro. Due to the...
Show moreThe retroviral capsid protein (CA) is derived from the cleavage of Gag polyprotein during the maturation process, and self-assembles into a polymorphic fullerene-like shell encasing the viral genome materials. The orthoretroviral CAs, for instance, Human Immunodeficiency Virus (HIV) and Rous Sarcoma Virus (RSV) CA, has little similarity in their sequence composition but a common 3D structure. They form distinct capsid assembly in vivo and a range of similar assemblies in vitro. Due to the substantial polymorphism, such assemblies are not amenable for conventional structural biology techniques such as X-ray diffraction crystallography and cryo-electron microscopy (cryo-EM). Solid-state NMR spectroscopy is the optimal platform to study these CA assemblies to attain site-specific structural and dynamic information. However, it is challenging to make signal assignments for such non-crystalline and large biomolecules as retroviral CA assemblies. In this study, we were to elucidate the assembly mechanism of retroviral capsids by applying the state-of-art solid-state NMR techniques on the RSV CA assembly system and establishing an atomistic resolution structural model. The RSV CA is the second most studied protein among the retroviral family after HIV that causes AIDS (acquired immune deficiency syndrome), but there is no atomistic model for RSV CA assemblies available.In this study, we showed that highly uniform tubular RSV CA assembly can be prepared. Screened by TEM, our tubular assembly showed sharp 6-fold symmetry under diffraction, illustrating the quasi-crystalline character. Subsequently we acquired a series of solid-state NMRivspectra for tubular RSV CA assembly, and completed chemical shift signal assignments with samples of various isotope labeling. Then, combining cryo-EM electron density map of tubular assembly of RSV CA with the secondary structures derived from solid-state NMR, we established an atomistic resolution structure model. In this model, we identified the residue-specific assembly interfaces. Interestingly, our model revealed the structural re-arrangements upon the assembly and suggested that the tubular assembly of RSV CA may take a different assembly pathway from that of HIV capsid.
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Date Issued
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2016
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Identifier
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CFE0006332, ucf:51572
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006332
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Title
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Local transient characterization of thermofluid heat transfer coefficient at solid-liquid nano-interfaces.
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Creator
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Mehrvand, Mehrdad, Putnam, Shawn, Peles, Yoav, Orlovskaya, Nina, Abdolvand, Reza, University of Central Florida
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Abstract / Description
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The demands for increasingly smaller, more capable, and higher power density technologies in microelectronics, energy, or aerospace systems have heightened the need for new methods to manage and characterize extreme heat fluxes (EHF). Microscale liquid cooling techniques are viewed as a promising solution for removing heat from high heat flux (HHF) systems. However, there have been challenges in physical understanding and predicting local thermal transport at the interface of micro and...
Show moreThe demands for increasingly smaller, more capable, and higher power density technologies in microelectronics, energy, or aerospace systems have heightened the need for new methods to manage and characterize extreme heat fluxes (EHF). Microscale liquid cooling techniques are viewed as a promising solution for removing heat from high heat flux (HHF) systems. However, there have been challenges in physical understanding and predicting local thermal transport at the interface of micro and nanoscale structures/devices due to ballistic effects and complex coupling of mass, momentum, and energy transport at the solid-liquid-vapor interfaces over multiple time and length scales. Moreover, it's challenging to experimentally validate new HHF models due to lack of high resolution techniques and measurements.This dissertation presents the use of a high spatiotemporal and temperature resolution measurement technique, called Time-domain Thermoreflectance (TDTR). TDTR is used to characterize the local heat transfer coefficient (HTC) of a water-cooled rectangular microchannel in a combined hot-spot heating and sub-cooled channel-flow configuration. Studies focused on room temperature, syringe-pumped single-and two-phase water flow in a ?480 ?m hydraulic diameter microchannel, where the TDTR pump heating laser induces local heat fluxes of ?0.5-2.5 KW/cm2 in the center of the microchannel on the surface of a 60-80 nm metal or alloy thin film transducer with hot-spot diameters of ?7-10 ?m. In the single-phase part, a differential measurement approach is developed by applying anisotropic version of the TDTR to predict local HTC using the measured voltage ratio parameter, and then fitting data to a thermal model for layered materials and interfaces. It's shown that thermal effusivity distribution of the water coolant over the hot-spot is correlated to the local HTC, where both the stagnant fluid (i.e., conduction and natural convection) and flowing fluid (i.e., forced convection) contributions are decoupled from each other. Measurements of the local enhancement in the HTC over the hot-spot are in good agreement with established Nusselt number correlations. For example, flow cooling results using a Ti metal wall support a maximum HTC enhancement via forced convection of ?1060(&)#177;190 kW/m2?K, where the well-established Nusselt number correlations predict ?900(&)#177;150 kW/m2?K.In the two-phase part, pump-probe beams are first used to construct the local pool and flow boiling curves at different heat fluxes and hot spot temperatures as a function of HTC enhancement. At a same heat flux level, it's observed that fluid flow enhances HTC by shifting heat transfer mechanism (or flow regime) from film boiling to nucleate boiling. Based on observations, it's hypothesized that beyond an EHF flow may reduce the bubble size and increase evaporation at the liquid-vapor interface on three-phase contact line, but it's unable to rewet and cool down the dry spot at the center due to the EHF. In the last part of two-phase experiments, transient measurements are performed at a specific heat flux to obtain thermal temporal fluctuations and HTC of a single bubble boiling and nucleation during its ebullition cycle. The total laser power is chosen to be between the minimum required to start subcooled nucleation and CHF of the pool boiling. This range is critical since within 10% change in heating flux, flow can have dramatic effect on HTC. Whenever the flow gets closer to the dry spot and passes through it (receding or advancing) HTC increases suddenly. This means that for very hot surfaces (or regions of wall dry-out), continuous and small bubbles on the order of thermal diffusion time and dry spot length scales respectively could be a reliable high heat flux cooling solution. This could be achieved by controlling the bubble size and frequency through geometry, surface structure and properties, and fluid's thermos-fluid properties.
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Date Issued
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2017
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Identifier
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CFE0006765, ucf:51832
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006765
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Title
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Manufacturing of Single Solid Oxide Fuel Cells.
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Creator
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Torres-Caceres, Jonathan, Orlovskaya, Nina, Xu, Yunjun, Das, Tuhin, University of Central Florida
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Abstract / Description
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Solid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials...
Show moreSolid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials and manufacturing methods is necessary to reduce costs and improve efficiency to make the technology commercially viable.The goal of the research is to optimize and simplify the production of single SOFCs using high performance ceramics. This includes the use of 8mol% Y2O3-ZrO2 (YSZ) and 10mol% Sc2O3-1mol%CeO2-ZrO2 (SCSZ) layered electrolytes which purport higher conductivity than traditional pure YSZ electrolytes. Prior to printing the electrodes onto the electrolyte, the cathode side of the electrolyte was coated with 20mol% Gd2O3-CeO2 (GDC). The GDC coating prevents the formation of a nonconductive La2Zr2O7 pyrochlore layer, which forms due to the interdiffusion of the YSZ electrolyte ceramic and the (La0.6Sr0.4)0.995Fe0.8Co0.2O3 (LSCF) cathode ceramic during sintering. The GDC layer was deposited by spin coating a suspension of 10wt% GDC in ethanol onto the electrolyte. Variation of parameters such as time, speed, and ramp rate were tested. Deposition of the electrodes onto the electrolyte surface was done by screen printing. Ink was produced using a three roll mill from a mixture of ceramic electrode powder, terpineol, and a pore former. The pore former was selected based on its ability to form a uniform well-connected pore matrix within the anode samples that were pressed and sintered. Ink development involved the production of different ratios of powder-to-terpineol inks to vary the viscosity. The different inks were used to print electrodes onto the electrolytes to gauge print quality and consistency. Cells were produced with varying numbers of layers of prints to achieve a desirable thickness. Finally, the densification behaviors of the major materials used to produce the single cells were studied to determine the temperatures at which each component needs to be sintered to achieve the desired density and to determine the order of electrode application, so as to avoid over-densification of the electrodes. Complete cells were tested at the National Energy Technology Laboratory in Morgantown, WV. Cells were tested in a custom-built test stand under constant voltage at 800(&)deg;C with 3% humidified hydrogen as the fuel. Both voltage-current response and impedance spectroscopy tests were conducted after initial startup and after 20 hours of operation. Impedance tests were performed at open circuit voltage and under varying loads in order to analyze the sources of resistance within the cell. A general increase in impedance was found after the 20h operation. Scanning electron micrographs of the cell microstructures found delamination and other defects which reduce performance. Suggestions for eradicating these issues and improving performance have been made.
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Date Issued
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2013
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Identifier
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CFE0004946, ucf:49641
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004946
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Title
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Aggregation of Squaraine Dye Derivatives in Solid State Spin-coated Thin Films.
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Creator
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Daoudi, Mohammed, Belfield, Kevin, Miles, Delbert, Campiglia, Andres, Bhattacharya, Aniket, Rex, Matthew, University of Central Florida
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Abstract / Description
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Squaraine dyes have been the subject of intensive studies due their unusual electronic properties that make them good candidates for a wide range of applications in various technological fields. They are particularly promising in nonlinear optics, bioimaging for labeling and sensing of biomolecules, as sensitizers for solar energy harvesting in solar cells and organic photovoltaics, two-photon absorbing materials, near-infrared (NIR) emitting fluorescent probes, second harmonic generation...
Show moreSquaraine dyes have been the subject of intensive studies due their unusual electronic properties that make them good candidates for a wide range of applications in various technological fields. They are particularly promising in nonlinear optics, bioimaging for labeling and sensing of biomolecules, as sensitizers for solar energy harvesting in solar cells and organic photovoltaics, two-photon absorbing materials, near-infrared (NIR) emitting fluorescent probes, second harmonic generation organic dyes, and sensitizers for photodynamic therapy among others. In this dissertation, the aggregation behaviors and features of several squaraine dye derivatives in solid state thin films were studied and reported.In the first chapter of the dissertation, three squaraine dye derivatives with two and four hydroxy groups and with different N-alkyl amino donor substituents were synthesized and used as models to study aggregation behavior. Their UV-vis absorption, thermal properties, and photoluminescence properties were determined. The models with four hydroxy substituents exhibited higher thermal stability and melt at higher temperature compared to the dye with only two hydroxy substituents due to increased hydrogen bonding. The UV-vis absorption and photoluminescence properties in liquid solution at room temperature were found to be similar.In the second chapter, the squaraine dyes, 2,4-bis [4-(N,N-di-n-pentylamino)-2-hydroxyphenyl] squaraine [SQC5(OH)2], 2,4-bis [4-(N,N-di-n-pentylamino)-2,4-hydroxyphenyl] squaraine [SQC5(OH)4 n], and 2,4-bis [4-(N,N-di-isopentylamino)-2,4-hydroxyphenyl] squaraine [SQC5(OH)4 b], where (")n(") and (")b(") stand for normal or linear and branched alkyl groups, respectively, were investigated to study their aggregation in solid state thin film form using UV-vis absorption spectroscopy. The investigation revealed significant differences in aggregation behaviors and features. The dye SQC5(OH)2 mainly exhibited J-type aggregation with an intense absorption band in the NIR region. In contrast, the SQC5(OH)4 n and SQC5(OH)4 b compounds mainly exhibited H-type aggregation, characterized by less intense and blue shifted absorption bands. The third chapter presents the kinetic study conducted on the squaraine dye derivative 2,4-bis [4-(N,N-di-n-pentylamino)-2-hydroxyphenyl] squaraine [SQC5(OH)2] in solid state spin-coated thin films. The study revealed the formation of J-aggregates with bands at 767 nm at room temperature. This aggregate was temperature dependent. It was transformed into H-aggregates as the temperature increased. The activation energy of the decay (transformation) process was found to be 91.2 kJ. The values of ?H and ?S are 88.4 kJ/mol and 48.2 J/K.mol, respectively, indicating the J-aggregate of SQC5(OH)2 was a kinetic product while the H-aggregate was thermondynamically more stable.
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Date Issued
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2015
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Identifier
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CFE0005778, ucf:50064
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0005778
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Title
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An assessment of ecological processes in the Apalachicola estuarine system, Florida.
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Creator
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Smar, Daina, Hagen, Scott, Wang, Dingbao, Weishampel, John, University of Central Florida
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Abstract / Description
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The following is a compilation of field data collected in 2011 and 2012 in Apalachicola, FL as part of a five year study assessing the ecological effects of sea level rise in the northern Gulf of Mexico. Many coastal communities, both natural and developed, will soon be working to mitigate the effects of sea level rise, if they are not already doing so. This thesis investigates the natural patterns of the Apalachicola estuarine system through the collection and analysis of in situ water,...
Show moreThe following is a compilation of field data collected in 2011 and 2012 in Apalachicola, FL as part of a five year study assessing the ecological effects of sea level rise in the northern Gulf of Mexico. Many coastal communities, both natural and developed, will soon be working to mitigate the effects of sea level rise, if they are not already doing so. This thesis investigates the natural patterns of the Apalachicola estuarine system through the collection and analysis of in situ water, sediment, and biomass samples. Additionally, results of the field samples are presented and recommendations for additional sampling are given. The field methods and procedures developed in this study were designed to be repeated in other estuaries to build upon the work that has been conducted in Apalachicola. Water samples were tested for total suspended solids (TSS) and compared against hydrodynamic (tidal circulation and streamflow) and meteorological (wind and precipitation) characteristics. Streamflow was determined to influence a seasonal base level concentration of TSS. Wind strength and direction consistently influenced small TSS concentration fluctuations, an effect amplified by the shallow nature of the estuary. Tidal circulation appeared to have minor influences on TSS concentration fluctuations within the base level concentration range. Precipitation appeared to influence large TSS concentration fluctuations; however, due to limited data collection during storm events, more data is required to conclusively state this. Sediment cores throughout the lower Apalachicola River revealed that coarse particles settled out in upstream areas while fine particles tended to stay in suspension until low energy areas in the lower portions of the river or marsh system were reached. Finally, biomass samples were used to develop regression models utilizing remotely sensed data to predict biomass density in marsh areas with unprecedented accuracy. The documented patterns of this system are to be used as inputs and validation points to update an existing hydrodynamic model and to aid in the coupling and development of sediment transport and marsh equilibrium models. The field campaign developed and implemented here provides a foundation for this novel coupled modeling effort of estuarine systems. From the 2011 and 2012 sampling conducted, it is apparent that Apalachicola can be modeled as a closed system with river inflow and sediment influx as boundary conditions. Forcing local conditions should accurately represent the system. Ultimately, these models will be used to simulate future sea level rise scenarios and will provide useful decision making tools to coastal managers. Future work will include replicating water sampling in subsequent wet and dry seasons in Apalachicola, FL to confirm observed trends, in addition to implementing this sampling in Grand Bay, MS and Weeks Bay, AL. Additional biomass samples will be taken to validate the strong correlations found between remotely sensed data and in situ samples. In similar studies, it is recommended that water samples be taken to adequately represent influences from tidal cycles and riverine inflow. It is also recommended that spatially distributed biomass samples be taken to validate regression models.
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Date Issued
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2012
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Identifier
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CFE0004602, ucf:49920
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004602
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Title
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Novel Fuel-producing Fungi and Methodologies for Increasing Fuel Production.
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Creator
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Wang, Yuemin, Harper, James, Bridge, Candice, Frazer, Andrew, Beazley, Melanie, Blair, Richard, University of Central Florida
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Abstract / Description
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An endophytic fungus Hypoxylon sp. (BS15) has recently been isolated and found to produce volatile organic compounds (VOCs) that have potential relevance as hydrocarbon fuels. In the work described here, the traditional refined carbohydrate (e.g., sucrose) diet source was replaced by simple sugars produced using a solvent free green chemistry mechanocatalytic method involving ball milling in the solid. BS15 is able to grow on this degraded cellulose as well as the more traditional potato...
Show moreAn endophytic fungus Hypoxylon sp. (BS15) has recently been isolated and found to produce volatile organic compounds (VOCs) that have potential relevance as hydrocarbon fuels. In the work described here, the traditional refined carbohydrate (e.g., sucrose) diet source was replaced by simple sugars produced using a solvent free green chemistry mechanocatalytic method involving ball milling in the solid. BS15 is able to grow on this degraded cellulose as well as the more traditional potato dextrose broth. The volatile compounds produced from both media were largely the same. Unfortunately, it is observed that long term in vitro growth of BS15 results in diminished VOC production. The VOC production was partially restored by cultivating BS15 in growth media containing finely ground woody tissue from the original host plant (Taxodium distichum). Extracts from this woody tissue were made by sequentially extracting with dichloromethane, methanol, and water with a goal of isolating VOC production modulators. Both the dichloromethane and water extracts place on bio-mimicking filter paper were found to modulate VOC production, while the methanol extract had no significant impact. Surprisingly, the woody tissue remaining after exhaustive extraction also acted as a VOC production modulator when combined with the growth media, with noticeable changes in the production of four compounds. This woody tissue also induced production of two compounds not observed in the original BS15 extract, and their changes are inheritable. Remarkably filter paper had the same modulating effect as exhaustively extracted woody tissue, suggesting the modulation was partially due to cellulose degradation products. Extraction of the maximum amounts of VOCs is desirable and here a comparison of solid phase extraction (SPE) and solid phase micro-extraction (SPME) techniques is made. This comparison involves two endophytes, BS15C and Streptomyces ambofaciens (SA 40053). The SPE technique is more effective in retaining compounds having lower vapor pressures and higher boiling points with nearly three to five times more VOC mass obtained versus SPME.
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Date Issued
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2019
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Identifier
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CFE0007552, ucf:52598
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0007552
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Title
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N MULTILAYER THIN FILM REACTIONS TO FORM L10 FEPT AND EXCHANGE SPRING MAGNETS.
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Creator
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Yao, Bo, Coffey, Kevin, University of Central Florida
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Abstract / Description
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FePt films with the L10 phase have potential applications for magnetic recording and permanent magnets due to its high magnetocrystalline anisotropy energy density. Heat treatment of n multilayer films is one approach to form the L10 FePt phase through a solid state reaction. This thesis has studied the diffusion and reaction of n multilayer films to form the L10 FePt phase and has used this understanding to construct exchange spring magnets. The process-structure-property relations of n...
Show moreFePt films with the L10 phase have potential applications for magnetic recording and permanent magnets due to its high magnetocrystalline anisotropy energy density. Heat treatment of n multilayer films is one approach to form the L10 FePt phase through a solid state reaction. This thesis has studied the diffusion and reaction of n multilayer films to form the L10 FePt phase and has used this understanding to construct exchange spring magnets. The process-structure-property relations of n multilayer films were systematically examined. The transmission electron microscopy (TEM) study of the annealed multilayers indicates that the Pt layer grows at the expense of Fe during annealing, forming a disordered fcc FePt phase by the interdiffusion of Fe into Pt. This thickening of the fcc Pt layer can be attributed to the higher solubilities of Fe into fcc Pt, as compared to the converse. For the range of film thickness studied, a continuous L10 FePt product layer that then thickens with further annealing is not found. Instead, the initial L10 FePt grains are distributed mainly on the grain boundaries within the fcc FePt layer and at the Fe/Pt interfaces and further transformation of the sample to the ordered L10 FePt phase proceeds coupled with the growth of the initial L10 FePt grains. A comprehensive study of annealed n films is provided concerning the phase fraction, grain size, nucleation/grain density, interdiffusivity, long-range order parameter, and texture, as well as magnetic properties. A method based on hollow cone dark field TEM is introduced to measure the volume fraction, grain size, and density of ordered L10 FePt phase grains in the annealed films, and low-angle X-ray diffraction is used to measure the effective Fe-Pt interdiffusivity. The process-structure-properties relations of two groups of samples with varying substrate temperature and periodicity are reported. The results demonstrate that the processing parameters (substrate temperature, periodicity) have a strong influence on the structure (effective interdiffusivity, L10 phase volume fraction, grain size, and density) and magnetic properties. The correlation of these parameters suggests that the annealed n multilayer films have limited nuclei, and the subsequent growth of L10 phase is very important to the extent of ordered phase formed. A correlation between the grain size of fcc FePt phase, grain size of the L10 FePt phase, the L10 FePt phase fraction, and magnetic properties strongly suggests that the phase transformation of fccL10 is highly dependent on the grain size of the parent fcc FePt phase. A selective phase growth model is proposed to explain the phenomena observed. An investigation of the influence of total film thickness on the phase formation of the L10 FePt phase in n multilayer films and a comparison of this to that of FePt co-deposited alloy films is also conducted. A general trend of greater L10 phase formation in thicker films was observed in both types of films. It was further found that the thickness dependence of the structure and of the magnetic properties in n multilayer films is much stronger than that in FePt alloy films. This is related to the greater chemical energy contained in n films than FePt alloy films, which is helpful for the L10 FePt phase growth. However, the initial nucleation temperature of n multilayers and co-deposited alloy films was found to be similar. An investigation of L10 FePt-based exchange spring magnets is presented based on our understanding of the L10 formation in n multilayer films. It is known that exchange coupling is an interfacial magnetic interaction and it was experimentally shown that this interaction is limited to within several nanometers of the interface. A higher degree of order of the hard phase is shown to increase the length scale slightly. Two approaches can be used to construct the magnets. For samples with composition close to stoichiometric L10 FePt, the achievement of higher energy product is limited by the average saturation magnetization, and therefore, a lower annealing temperature is beneficial to increase the energy product, allowing a larger fraction of disordered phase. For samples with higher Fe concentration, the (BH)max is limited by the low coercivity of annealed sample, and a higher annealing temperature is beneficial to increase the energy product.
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Date Issued
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2008
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Identifier
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CFE0002416, ucf:47749
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002416
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Title
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STRUCTURAL EVOLUTION IN MECHANICALLY ALLOYED FE-BASED POWDER SYSTEMS.
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Creator
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Patil, Umesh, Suryanarayan, Challapalli, University of Central Florida
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Abstract / Description
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A systematic study of iron-based binary and multi-component alloys was undertaken to study the structural evolution in these powders as a function of milling time during mechanical alloying. Blended elemental powders of Fe100-XBX (where x = 5, 10, 17, 20, 22, 25, 37.5 and 50 at. %) and a bulk metallic glass (BMG) composition (Fe60Co8Zr10Mo5W2B15) were subjected to mechanical alloying in a SPEX 8000 mixer mill. X-ray diffraction technique was employed to study the phase evolution, crystallite...
Show moreA systematic study of iron-based binary and multi-component alloys was undertaken to study the structural evolution in these powders as a function of milling time during mechanical alloying. Blended elemental powders of Fe100-XBX (where x = 5, 10, 17, 20, 22, 25, 37.5 and 50 at. %) and a bulk metallic glass (BMG) composition (Fe60Co8Zr10Mo5W2B15) were subjected to mechanical alloying in a SPEX 8000 mixer mill. X-ray diffraction technique was employed to study the phase evolution, crystallite size, lattice strain and also to determine the crystal structure(s) of the phases. Depending on the milling time, formation of supersaturated solid solutions, intermetallics, and amorphous phases was noted in the binary Fe-B powder mixtures. A maximum of about 22 at. % B was found to dissolve in Fe in the solid state, and formation of FeB and Fe2B intermetallics was noted in some of the powder blends. However, an interesting observation that was made, for the first time, related to the formation of a crystalline phase on continued milling of the amorphous powder in the BMG composition. This phenomenon, termed mechanical crystallization, has been explored. Reasons for the mechanical crystallization of the amorphous powder using the X-ray diffraction and electron microscopy methods have been discussed. External heat treatments of the milled powder were also conducted to study the complete crystallization behavior of the amorphous phase. Preliminary attempts were made to consolidate the milled BMG powder to bulk shape by hot isostatic pressing (HIP) and magnetic compaction techniques. Full densification was not achieved. Nanoindentation and microhardness tests were performed to characterize the mechanical properties of the glassy alloy. Nanoindentation results gave an elastic modulus of 59 GPa, lower than the expected value of 184 GPa; due to the presence of porosity in the consolidated sample. Optimization of the consolidation parameters is required to achieve a fully dense material.
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Date Issued
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2005
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Identifier
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CFE0000868, ucf:46649
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000868
Pages