Current Search: Aluminum (x)
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Title
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PROCESSING, MICROSTRUCTURAL AND MECHANICAL CHARACTERIZATION OF MECHANICALLY ALLOYED AL-ALUMINA NANOCOMPOSITES.
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Creator
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Katiyar, Pushkar, SURYANARAYANA, C., University of Central Florida
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Abstract / Description
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Aluminum-alumina nanocomposites were synthesized using mechanical alloying of blended component powders of pure constituents. This study was performed on various powder mixtures with aluminum as the matrix and alumina as the reinforcement with volume fractions of 20, 30, and 50 % and Alumina particle sizes of 50 nm, 150 nm, and 5 µm. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used for the crystal structure and microstructural characterization of the...
Show moreAluminum-alumina nanocomposites were synthesized using mechanical alloying of blended component powders of pure constituents. This study was performed on various powder mixtures with aluminum as the matrix and alumina as the reinforcement with volume fractions of 20, 30, and 50 % and Alumina particle sizes of 50 nm, 150 nm, and 5 µm. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used for the crystal structure and microstructural characterization of the powders at different stages of milling. Alumina powders with 50 nm and 150 nm particle size were predominantly of gamma-type, while Alumina of 5 µm size was of alpha-type. The main goal was to achieve uniform distribution of the alumina ceramic particles in the Al matrix, which was achieved on milling for 24 h in a SPEX mill or 100 h in a Fritsch Pulverisette planetary ball mill. The powders were consolidated in two stages: pre-compaction at room temperature followed by vacuum hot pressing (VHP) or hot isostatic pressing (HIP) techniques to a fully dense condition. The effect of reinforcement particle size and volume fraction on the stress-strain response, elastic modulus and yield strength of the composites was investigated. Nanoindentation and compression tests were performed to characterize the composite material. Yield strength of 515 MPa, compressive strength of 685 MPa and elastic modulus of 36 GPa were obtained from compression tests. Nanoindentation results gave the yield strength of 336 MPa, maximum shear stress of 194 MPa and an elastic modulus of 42 GPa. The low elastic modulus values obtained from the above tests might be because of localized yielding possibly due to residual stresses.
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Date Issued
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2004
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Identifier
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CFE0000128, ucf:46193
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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/CFE0000128
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Title
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Aging Characteristics of an Aluminum-4.5% Copper-1.5% Magnesium Alloy.
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Creator
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Sulouff, Robert E., Smith, William F., Engineering
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Abstract / Description
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Florida Technological University College of Engineering Thesis; The effects of quenching conditions, single-step and two-step aging treatments on the tensile properties of an AL-4.5%Cu-1.5%Mg alloy has been investigated. Results indicate that two distinctly different precipitates of GPB and S' form during aging. Single-step aging at 140°C, 160°C and 190°C indicated that 24 hours at 160°C produced optimum strength (67 ksi UTS). Two-step aging for 3 days at 140°C plus 190°C resulted in a...
Show moreFlorida Technological University College of Engineering Thesis; The effects of quenching conditions, single-step and two-step aging treatments on the tensile properties of an AL-4.5%Cu-1.5%Mg alloy has been investigated. Results indicate that two distinctly different precipitates of GPB and S' form during aging. Single-step aging at 140°C, 160°C and 190°C indicated that 24 hours at 160°C produced optimum strength (67 ksi UTS). Two-step aging for 3 days at 140°C plus 190°C resulted in a slight increase in strength over single step aging at 190°C. Slow (oil) quenching as well as direct quenching improved the tensile properties when aged at 190°C. Reversion occurred slowly over the temperature range 250°C to 350°C.
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Date Issued
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1977
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Identifier
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CFR0011985, ucf:53095
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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/CFR0011985
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Title
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STRESS INTENSITY FACTOR DEPENDENCE OF HG-AL LIQUID METAL EMBRITTLEMENT.
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Creator
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Keller, Scott, Gordon, Ali, University of Central Florida
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Abstract / Description
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When high strength aluminum alloys are subjected to liquid metals, physical and chemical reactions ensue resulting in what is known as liquid metal embrittlement (LME). A subset of environmentally-assisted cracking, LME is exhibited when a liquid metal, e.g. Hg or Ga, comes into intimate contact with a solid metal having significant susceptibility. As mechanical loads are applied, the interaction between the two metals results in a reduction in the flow properties of the solid metal. Several...
Show moreWhen high strength aluminum alloys are subjected to liquid metals, physical and chemical reactions ensue resulting in what is known as liquid metal embrittlement (LME). A subset of environmentally-assisted cracking, LME is exhibited when a liquid metal, e.g. Hg or Ga, comes into intimate contact with a solid metal having significant susceptibility. As mechanical loads are applied, the interaction between the two metals results in a reduction in the flow properties of the solid metal. Several theories have been proposed to identify the underlying microstructural failure mechanism; however, none have been widely accepted, as failures can typically incorporate features common to several failure theories. In an effort to confirm, extend or replace the physically-based theories, fracture mechanics experiments on Al 7075T651 in liquid mercury have been conducted. Experiments were conducted in a custom environmental chamber capable of exposing specimens to liquid environments while applying a mechanical load. Through both plane-strain fracture and stress intensity factor-dependent (SIF) tests, fracture toughness values along with incubation periods were analyzed and provided data for a load-based theory of LME. These mechanical test data, along with metallographic analysis, show that the phenomena of LME is both strongly time- and SIF-dependent.
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Date Issued
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2009
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Identifier
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CFE0002893, ucf:48033
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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/CFE0002893
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Title
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Aging Characteristics of Al-4.5%Cu-1.4%Mg-0.5%Ag.
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Creator
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White, James Kelly, Smith, William F., Engineering
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Abstract / Description
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Florida Technological University College of Engineering Thesis; The effects of single-step and two-step aging treatments on the tensile properties of an A1-4.5%Cu-1.4%Mg- 0.5%Ag alloy have been investigated. Results showed that a maximum ultimate tensile strength of 75 ksi can be attained by single-step aging 24 hr at 170°C. The two-step aging treatments consisting of first aging one week at 80°C followed by aging at 160° and 190°C led to lower strength properties than simple one-step aging....
Show moreFlorida Technological University College of Engineering Thesis; The effects of single-step and two-step aging treatments on the tensile properties of an A1-4.5%Cu-1.4%Mg- 0.5%Ag alloy have been investigated. Results showed that a maximum ultimate tensile strength of 75 ksi can be attained by single-step aging 24 hr at 170°C. The two-step aging treatments consisting of first aging one week at 80°C followed by aging at 160° and 190°C led to lower strength properties than simple one-step aging. Reversion treatments applied to fully age-hardened alloy resulted in an almost progressive loss of strength in the 250° to 375° range.
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Date Issued
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1977
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Identifier
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CFR0003473, ucf:53038
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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/CFR0003473
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Title
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RECOVERY OF HYDROGEN AND HELIUM FROM THEIR MIXTURES USING METAL HYDRIDES.
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Creator
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Oztek, Muzaffer, Hampton, Michael, University of Central Florida
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Abstract / Description
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Waste streams of hydrogen and helium mixtures are produced at the Kennedy Space Center during purging of the hydrogen systems and supply lines. This process is done prior to and after hydrogen servicing. The purged waste gases are lost to the atmosphere, resulting in an annual loss of 2 million and 0.1 million standard cubic meters of helium and hydrogen, respectively. Recovery of these gases will have an economic benefit. Metals, alloys, and intermetallics are known to react with hydrogen in...
Show moreWaste streams of hydrogen and helium mixtures are produced at the Kennedy Space Center during purging of the hydrogen systems and supply lines. This process is done prior to and after hydrogen servicing. The purged waste gases are lost to the atmosphere, resulting in an annual loss of 2 million and 0.1 million standard cubic meters of helium and hydrogen, respectively. Recovery of these gases will have an economic benefit. Metals, alloys, and intermetallics are known to react with hydrogen in favorable conditions; therefore, they have the possibility of serving as separating and recovery agents. In this study, Mg2Ni, VTiNi and LaNi5 were studied for the separation of H2 from He, using differential scanning calorimetry and thermal volumetric analysis. The ability of LaNi5 to react with hydrogen reversibly at room temperature was verified, and further analysis focused on this compound. Size reduction and activation of LaNi5 by mechanical milling was investigated using different milling parameters for the purpose of activating the material for hydrogen absorption. Because it has been shown that addition of aluminum to LaNi5 resulted in improved hydriding and dehydriding properties, that system was studied further here. In this study, aluminum was added to LaNi5 by mechanical milling. Hydriding properties and elemental compositions of the samples were determined afterwards. The hydrogen absorption rate and capacity were compared to that of LaNi5. Both LaNi5 and its Al doped derivatives exhibited a reduced rate of hydrogen uptake and a reduced hydrogen capacity in the presence of helium. The effects of coating the samples with either gold-palladium or platinum were investigated. It was observed that coating the samples with Pt reduced the negative effect of He, whereas AuPd coating did not have any effect. Larger scale studies were done using a continuous U-tube hydride reactor, built and tested for separation of H2¬ from a 20:80 H2:He mixture. The amount of hydrogen retained in the bed was determined and found to be less than that for the batch systems.
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Date Issued
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2005
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Identifier
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CFE0000660, ucf:46507
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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/CFE0000660
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Title
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IMPURITY AND INTERDIFFUSION IN THE MAGNESIUM-ALUMINUM SYSTEM.
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Creator
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Brennan, Sarah, Sohn, Yongho, University of Central Florida
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Abstract / Description
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Magnesium alloys offer a base of lightweight engineering materials for electronic, military and transportation applications where weight reduction is crucial for higher efficiency. Understanding fundamental diffusion behavior in Mg alloys elicits better materials properties through the optimization of processing techniques and heat treatments, whose material responses are affected by diffusion. The main objective of this study is to provide a clear, comprehensive description of the diffusion...
Show moreMagnesium alloys offer a base of lightweight engineering materials for electronic, military and transportation applications where weight reduction is crucial for higher efficiency. Understanding fundamental diffusion behavior in Mg alloys elicits better materials properties through the optimization of processing techniques and heat treatments, whose material responses are affected by diffusion. The main objective of this study is to provide a clear, comprehensive description of the diffusion behavior in the technically important magnesium-aluminum binary metallic system. In this study, diffusion in the Mg-Al system was observed through solid diffusion couples and thin film specimens in the temperature range of 673-523K. The formation and growth of the intermetallic phases, [two]-Mg2Al3 and [three]-Mg17Al12, and the absence of the [micro]-Mg23Al30 phase was observed. The [two]-Mg2Al3 phase grew thicker, had higher parabolic growth constants and lower activation energy for growth. Concentration-dependent interdiffusion coefficients were determined using the Boltzmann-Matano method. Interdiffusion in the [two]-Mg2Al3 phase was the highest, followed by the [three]-Mg17Al12 phase, the Al solid solution and the Mg solid solution. Intrinsic diffusion coefficients at the marker plane composition of 38 at.% Mg in the [two]-Mg2Al3 were determined from Heumann's method for Mg and Al, for which Al was higher. Extrapolations of the impurity diffusion coefficients in both terminal solid solutions were made and compared to available literature data. The thermodynamic factor, tracer diffusivity and atomic mobility of Mg and Al at the marker plane concentration were estimated using Mg activities in the [two]-Mg2Al3 available from literature. The impurity diffusion of Al and self-diffusion of the stable isotope, 25Mg, in polycrystalline Mg was measured from thin film specimens via depth profiling using secondary ion mass spectrometry. The Al impurity diffusion observed is compared to the extrapolations from the parallel interdiffusion study. The self-diffusion measurements are compared to reported literature values and were observed to be significantly higher. Several reasons for the observed difference in the magnitude of diffusivities are discussed.
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Date Issued
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2011
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Identifier
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CFE0003984, ucf:48678
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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/CFE0003984
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Title
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Quantification of the Effect of Degassing on the Microstructure, Chemistry and Estimated Strength of Nanocrystalline AA5083 Powder.
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Creator
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Hofmeister, Clara, Sohn, Yongho, Challapalli, Suryanarayana, Coffey, Kevin, University of Central Florida
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Abstract / Description
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Degassing is a critical heat treatment process in aluminum powder metallurgy, where powders are subjected to high temperature in vacuum to remove volatile gaseous species absorbed in and adsorbed on powders. For cryomilled aluminum alloy powders with nanoscale features, degassing can cause accelerated microstructural and chemical changes including removal of volatiles, grain growth, dislocation annihilation, and formation of dispersoids. These changes can significantly alter the mechanical...
Show moreDegassing is a critical heat treatment process in aluminum powder metallurgy, where powders are subjected to high temperature in vacuum to remove volatile gaseous species absorbed in and adsorbed on powders. For cryomilled aluminum alloy powders with nanoscale features, degassing can cause accelerated microstructural and chemical changes including removal of volatiles, grain growth, dislocation annihilation, and formation of dispersoids. These changes can significantly alter the mechanical behavior of consolidated components based on their contributions to strength. In this study, cryomilled AA5083 (0.4 wt.% Mn; 4.5 wt.% Mg; minor Si, Fe, Cu, Cr, Zn, Ti; balance Al) powders were degassed at 200, 300, 350, 410 and 500(&)deg;C at a ramp rate of 68.3 (&)deg;C?hr-1 for a soak time of 8 hours with a vacuum at or below 6.5 x 10-3 Pa. Grain size, dislocation density and dispersoid phase constituents were examined as a function of degassing temperature by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, equipped with high angle annular dark field detector and X-ray energy dispersive spectroscopy. Inert gas fusion and thermal conductivity analysis were employed to determine the oxygen, nitrogen and hydrogen concentrations as a function of degassing temperature. Grain size in as-cryomilled powders (21 ~ 34 nm) increased as a function of degassing temperature, and reached a maximum value of 70 ~ 80 nm for powders degassed at 500(&)deg;C for 8 hours. The dislocation density of 1.11 x 1015 m-2 in as-cryomilled powders decreased to 1.56 x 1014 m-2 for powders degassed at 500(&)deg;C for 8 hours. The Al6(MnFeCr) phase was the most commonly observed dispersoid, mostly on samples degassed at or above 300(&)deg;C. Volume fraction increased with degassing temperature up to 5 vol.% and the size of the dispersoids grew up to ~ 280 nm. Oxygen and nitrogen content after cryomilling were unaffected by the change in degassing temperature, but the hydrogen content decreased and reached a minimum of 45 (&)#177; 3.16 ppm for cryomilled powders degassed at 500(&)deg;C for 8 hours. Grain growth was quantitatively analyzed based on the general grain growth formula and Burke's model in the presence of pinning forces. Degassing occurred in two different kinetic regimes: Harrison A kinetics at higher temperatures and Harrison B in the lower with a transition temperature of about 287(&)deg;C. Burke's model exhibited a poor fit to the experimental results in higher temperature regime. Desorption of impurities during degassing was analyzed using Fickian diffusion in a spherical coordinate system and an empirical expression based on the exponential decay of average concentration. The activation energy for degassing was estimated to be 16.2 (&)#177; 1.5 kJ?mol-1. Evolutions in composition and microstructure in cryomilled powders as a function of degassing temperature were further analyzed and quantitatively correlated to the strengthening mechanisms of solid solution, grain size reduction (i.e., Hall-Petch), dislocation forest and Orowan. For consolidated AA5083 derived from cryomilled powders, strengthening by grain size reduction was the dominant mechanism of strengthening.
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Date Issued
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2016
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Identifier
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CFE0006461, ucf:51426
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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/CFE0006461
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Title
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A Comparison of Aluminum and Iron-based Coagulants for Treatment of Surface Water in Sarasota County, Florida.
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Creator
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Yonge, David, Duranceau, Steven, Randall, Andrew, Cooper, Charles, University of Central Florida
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Abstract / Description
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In this research, five different coagulants were evaluated to determine their effectiveness at removing turbidity, color and dissolved organic carbon (DOC) from a surface water in Sarasota County, Florida. Bench-scale jar tests that simulated conventional coagulation, flocculation, and sedimentation processes were used. Iron-based coagulants (ferric chloride and ferric sulfate) and aluminum-based coagulants (aluminum sulfate, polyaluminum chloride (PACl) and aluminum chlorohydrate (ACH)) were...
Show moreIn this research, five different coagulants were evaluated to determine their effectiveness at removing turbidity, color and dissolved organic carbon (DOC) from a surface water in Sarasota County, Florida. Bench-scale jar tests that simulated conventional coagulation, flocculation, and sedimentation processes were used. Iron-based coagulants (ferric chloride and ferric sulfate) and aluminum-based coagulants (aluminum sulfate, polyaluminum chloride (PACl) and aluminum chlorohydrate (ACH)) were used to treat a highly organic surface water supply (DOC ranging between 10 and 30 mg/L), known as the Cow Pen Slough, located within central Sarasota County, Florida. Isopleths depicting DOC and color removal efficiencies as a function of both pH and coagulant dose were developed and evaluated. Ferric chloride and ACH were observed to obtain the highest DOC (85% and 70%, respectively) and color (98% and 97%, respectively) removals at the lowest dose concentrations (120 mg/L and 100 mg/L, respectively). Ferric sulfate was effective at DOC removal but required a higher concentration of coagulant and was the least effective coagulant at removing color. The traditional iron-based coagulants and alum had low turbidity removals and they were often observed to add turbidity to the water. PACl and ACH had similar percent removals for color and turbidity achieving consistent percent removals of 95% and 45%, respectively, but PACl was less effective than ACH at removing organics. Sludge settling curves, dose-sludge production ratios, and settling velocities were determined at optimum DOC removal conditions for each coagulant. Ferric chloride was found to have the highest sludge settling rate but also produced the largest sludge quantities. Total trihalomethane formation potential (THMFP) was measured for the water treated with ferric chloride and ACH. As with DOC removal, ferric chloride yielded a higher percent reduction with respect to THMFP.
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Date Issued
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2012
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Identifier
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CFE0004621, ucf:49936
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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/CFE0004621
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Title
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Development of Nitrogen Concentration During Cryomilling of Aluminum Composites.
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Creator
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Hofmeister, Clara, Sohn, Yongho, Suryanarayana, Challapalli, Coffey, Kevin, University of Central Florida
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Abstract / Description
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The ideal properties of a structural material are light weight with extensive strength and ductility. A composite with high strength and tailorable ductility was developed consisting of nanocrystalline AA5083, boron carbide and coarser grained AA5083. The microstructure was determined through optical microscopy and transmission electron microscopy. A technique was developed to determine the nitrogen concentration of an AA5083 composite from secondary ion mass spectrometry utilizing a nitrogen...
Show moreThe ideal properties of a structural material are light weight with extensive strength and ductility. A composite with high strength and tailorable ductility was developed consisting of nanocrystalline AA5083, boron carbide and coarser grained AA5083. The microstructure was determined through optical microscopy and transmission electron microscopy. A technique was developed to determine the nitrogen concentration of an AA5083 composite from secondary ion mass spectrometry utilizing a nitrogen ion-implanted standard. Aluminum nitride and amorphous nitrogen-rich dispersoids were found in the nanocrystalline aluminum grain boundaries. Nitrogen concentration increased as a function of cryomilling time up to 72hours. A greater nitrogen concentration resulted in an enhanced thermal stability of the nanocrystalline aluminum phase and a resultant increase in hardness. The distribution of the nitrogen-rich dispersoids may be estimated considering their size and the concentration of nitrogen in the composite. Contributions to strength and ductility from the Orowan relation can be more accurately modeled with the quantified nitrogen concentration.
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Date Issued
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2013
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Identifier
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CFE0004864, ucf:49702
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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/CFE0004864
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Title
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DESIGN, FABRICATION, AND TESTING OF HIGH-TRANSPARENCY DEEP ULTRA-VIOLETCONTACTS USING SURFACE PLASMON COUPLING IN SUBWAVELENGTH ALUMINUM MESHES.
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Creator
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Mazuir, Clarisse, Schoenfeld, Winston, University of Central Florida
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Abstract / Description
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The present work aims at enhancing the external quantum efficiencies of ultra-violet (UV) sensitive photodetectors (PDs) and light emitting diodes (LEDs)for any light polarization. Deep UV solid state devices are made out of AlGaN or MgZnO and their performances suffer from the high resistivity of their p-doped regions. They require transparent p-contacts; yet the most commonly used transparent contacts have low transmission in the UV: indium tin oxide (ITO) and nickel-gold (Ni/Au 5/5 nms)...
Show moreThe present work aims at enhancing the external quantum efficiencies of ultra-violet (UV) sensitive photodetectors (PDs) and light emitting diodes (LEDs)for any light polarization. Deep UV solid state devices are made out of AlGaN or MgZnO and their performances suffer from the high resistivity of their p-doped regions. They require transparent p-contacts; yet the most commonly used transparent contacts have low transmission in the UV: indium tin oxide (ITO) and nickel-gold (Ni/Au 5/5 nms) transmit less than 50% and 30% respectively at 300 nm. Here we investigate the use of surface plasmons (SPs) to design transparent p-contacts for AlGaN devices in the deep UV region of the spectrum. The appeal of using surface plasmon coupling arose from the local electromagnetic field enhancement near the metal surface as well as the increase in interaction time between the field and semiconductor if placed on top of a semiconductor. An in/out-coupling mechanism is achieved by using a grating consisting of two perpendicularly oriented sets of parallel aluminum lines with periods as low as 250 nm. The incident light is first coupled into SPs at the air/aluminum interface which then re-radiate at the aluminum/AlGaN interface and the photons energy is transferred to SP polaritons (SPPs) and back to photons. High transmission can be achieved not only at normal incidence but for a wider range of incident angles. A finite difference time domain (FDTD) package from R-Soft was used to simulate and design such aluminum gratings with transparency as high as 100% with tunable peak wavelength, bandwidth and angular acceptance. A rigorous coupled wave analysis (RCWA) was developed in Matlab to validate the FDTD results. The high UV transparency meshes were then fabricated using an e-beam assisted lithography lift-off process. Their electrical and optical properties were investigated. The electrical characterization was very encouraging; the sheet resistances of these meshes were lower than those of the conventionally used transparent contacts. The optical transmissions were lower than expected and the causes for the lower measurements have been investigated. The aluminum oxidation, the large metal grain size and the line edge roughness were identified as the main factors of inconsistency and solutions are proposed to improve these shortcomings. The effect of aluminum oxidation was calculated and the passivation of aluminum with SiO2 was evaluated as a solution. A cold deposition of aluminum reduced the aluminum grain size from 60 nm to 20 nm and the roughness from 5 nm to 0.5 nm. Furthermore, replacing the conventional lift-off process by a dry back-etch process led to much smoother metal line edges and much high optical transparency. The optical measurements were consistent with the simulations. Therefore, reduced roughness and smooth metal line edges were found to be especially critical considerations for deep UV application of the meshes.
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Date Issued
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2011
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Identifier
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CFE0003645, ucf:48893
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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/CFE0003645
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Title
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Interdiffusion and Impurity Diffusion in Magnesium Solid Solutions.
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Creator
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Kammerer, Catherine, Sohn, Yongho, Coffey, Kevin, Suryanarayana, Challapalli, Gordon, Ali, University of Central Florida
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Abstract / Description
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Magnesium, being lightweight, offers potential to be developed into extensive structural applications. The transportation segment has particular interest in Mg and Mg alloy for applications where reduced vehicle weight is proportional to increased fuel efficiency. Aluminum and zinc are two of the most common alloying elements in commercial Mg alloys. They improve the physical properties of Mg through solid solution strengthening and precipitation hardening. Diffusion plays a key role in the...
Show moreMagnesium, being lightweight, offers potential to be developed into extensive structural applications. The transportation segment has particular interest in Mg and Mg alloy for applications where reduced vehicle weight is proportional to increased fuel efficiency. Aluminum and zinc are two of the most common alloying elements in commercial Mg alloys. They improve the physical properties of Mg through solid solution strengthening and precipitation hardening. Diffusion plays a key role in the kinetics of and microstructural development during solidification and heat treatment. However, there is limited diffusion data available for Mg and Mg alloys. In particular, because Al is mono-isotopic, tracer diffusion data is not available. Interdiffusion of Mg solid solution with Zn also does not exist in literature. The diffusional interaction of Al and Zn in Mg solid solution at temperatures ranging from 623 (-) 723K was examined using solid-to-solid diffusion couple method. The objective of this thesis is two-fold: first, is the examination of interdiffusion in the Mg solid solution phase of the binary Mg-Al and Mg-Zn systems; second, is to explore non-conventional analytical methods to determine impurity diffusion coefficients. The quality of diffusion bonding was examined by optical microscopy and scanning electron microscopy with X-ray energy dispersive spectroscopy, and concentration profiles were determined using electron probe microanalysis with pure standards and ZAF matrix correction. Analytical methods of concentration profiles based on Boltzmann-Matano analysis for binary alloys are presented along with compositional dependent interdiffusion coefficients. As the concentration of Al or Zn approaches the dilute ends, an analytical approach based on the Hall method was employed to estimate the impurity diffusion coefficients.Zinc was observed to diffuse faster than Al, and in fact, the impurity diffusion coefficient of Al was smaller than the self-diffusion coefficient of Mg. In the Mg solid solution with Al, interdiffusion coefficients increased by an order of magnitude with an increase in Al concentration. Activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg solid solution with Al was determined to be 186.8 KJ/mole and 7.69 x 10-1 m^2/sec. On the other hand, in the Mg solid solution with Zn, interdiffusion coefficients did not vary significantly as a function of Zn concentration. Activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg solid solution with Zn was determined to be 129.5 KJ/mole and 2.67 x 10-4 m^2/sec. Impurity diffusion coefficients of Al in Mg was determined to have activation energy and pre-exponential factor of 144.1 KJ/mole and 1.61 x 10-4 m^2/sec. Impurity diffusion coefficients of Zn in Mg was determined to have activation energy and pre-exponential factor of 109.8 KJ/mole and 1.03 x 10-5 m^2/sec. Temperature and composition-dependence of interdiffusion coefficients and impurity diffusion coefficients are examined with respect to reported values in literature, thermodynamic factor, ?, diffusion mechanisms in hexagonal close packed structure, and experimental uncertainty.
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Date Issued
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2013
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Identifier
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CFE0004699, ucf:49851
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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/CFE0004699
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Title
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The Influence of Alloying Additions on Diffusion and Strengthening of Magnesium.
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Creator
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Kammerer, Catherine, Sohn, Yongho, Coffey, Kevin, Challapalli, Suryanarayana, Gordon, Ali, University of Central Florida
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Abstract / Description
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Magnesium alloys are being developed as advanced materials for structural applications where reduced weight is a primary motivator. Alloying can enhance the properties of magnesium without significantly affecting its density. Essential to alloy development, inclusive of processing parameters, is knowledge of thermodynamic, kinetic, and mechanical behavior of the alloy and its constituents. Appreciable progress has been made through conventional development processes, but to accelerate...
Show moreMagnesium alloys are being developed as advanced materials for structural applications where reduced weight is a primary motivator. Alloying can enhance the properties of magnesium without significantly affecting its density. Essential to alloy development, inclusive of processing parameters, is knowledge of thermodynamic, kinetic, and mechanical behavior of the alloy and its constituents. Appreciable progress has been made through conventional development processes, but to accelerate development of suitable wrought Mg alloys, an integrated Materials Genomic approach must be taken where thermodynamics and diffusion kinetic parameters form the basis of alloy design, process development, and properties-driven applications.The objective of this research effort is twofold: first, to codify the relationship between diffusion behavior, crystal structure, and mechanical properties; second, to provide fundamental data for the purpose of wrought Mg alloy development. Together, the principal deliverable of this work is an advanced understanding of Mg systems. To that end, the objective is accomplished through an aggregate of studies. The solid-to-solid diffusion bonding technique is used to fabricate combinatorial samples of Mg-Al-Zn ternary and Mg-Al, Mg-Zn, Mg-Y, Mg-Gd, and Mg-Nd binary systems. The combinatorial samples are subjected to structural and compositional characterization via Scanning Electron Microscopy with X-ray Energy Dispersive Spectroscopy, Electron Probe Microanalysis, and analytical Transmission Electron Microscopy. Interdiffusion in binary Mg systems is determined by Sauer-Freise and Boltzmann-Matano methods. Kirkaldy's extension of the Boltzmann-Matano method, on the basis of Onsager's formalism, is employed to quantify the main- and cross-interdiffusion coefficients in ternary Mg solid solutions. Impurity diffusion coefficients are determined by way of the Hall method. The intermetallic compounds and solid solutions formed during diffusion bonding of the combinatorial samples are subjected to nanoindentation tests, and the nominal and compositionally dependent mechanical properties are extracted by the Oliver-Pharr method.In addition to bolstering the scantly available experimental data and first-principles computations, this work delivers several original contributions to the state of Mg alloy knowledge. The influence of Zn concentration on Al impurity diffusion in binary Mg(Zn) solid solution is quantified to impact both the pre-exponential factor and activation energy. The main- and cross-interdiffusion coefficients in the ternary Mg solid solution of Mg-Al-Zn are reported wherein the interdiffusion of Zn is shown to strongly influence the interdiffusion of Mg and Al. A critical examination of rare earth element additions to Mg is reported, and a new phase in thermodynamic equilibrium with Mg-solid solution is identified in the Mg-Gd binary system. It is also demonstrated that Mg atoms move faster than Y atoms. For the first time the mechanical properties of intermetallic compounds in several binary Mg systems are quantified in terms of hardness and elastic modulus, and the influence of solute concentration on solid solution strengthening in binary Mg alloys is reported. The most significant and efficient solid solution strengthening is achieved by alloying Mg with Gd. The Mg-Nd and Mg-Gd intermetallic compounds exhibited better room temperature creep resistance than intermetallic compounds of Mg-Al. The correlation between the concentration dependence of mechanical properties and atomic diffusion is deliberated in terms of electronic nature of the atomic structure.
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Date Issued
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2015
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Identifier
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CFE0005815, ucf:50043
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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/CFE0005815