Department of Metallurgical and Materials Engineering
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Item The recovery of the by-products of coal. A monograph describing the Semet-Solvay By-Products Plant and processes at Holt, Ala.(University of Alabama Libraries, 1919) Glazner, John Frank; University of Alabama TuscaloosaA hundred years of development have passed since the streets of the city of London were first lighted with coal gas. This beginning of preparing coal gas by the distillation of cial has been expanded and developed into our modern great by-products recovery industries. The history of these years plainly shows how the proper utilization of by-products can revolutionize an industry. No attention was given to the recovery of by-products of coal as a factor in reducing the cost of production, when coal gas was produced first by the distillation of coal. Special laws were enacted in England at one time to prevent the contamination of streams and lakes with tar. We are now beginning to realize how wasteful our methods of coking coal have been and how necessary it is to conserve our supplies of fuel.Item Lattice Expansion in Nanocrystalline Niobium Thin Films(2003-04-09) Banerjee, R.; Sperling, E. A.; Thompson, G. B.; Fraser, H. L.; Bose, S.; Ayyub, P.; University of Alabama TuscaloosaHigh-purity nanocrystalline niobium (Nb) thin films have been deposited using high-pressure magnetron sputter deposition. Increasing the pressure of the sputtering gas during deposition has systematically led to reduced crystallite sizes in these films. Based on x-ray and electron diffraction results, it is observed that the nanocrystalline Nb films exhibit a significantly large lattice expansion with reduction in crystallite size. There is however, no change in the bcc crystal structure on reduction in crystallite size to below 5 nm. The lattice expansion in nanocrystalline Nb has been simulated by employing a recently proposed model based on linear elasticity and by appropriately modifying it to incorporate a crystallite-size-dependent width of the grain boundary.Item Tuning phase stability in nanocomposite multilayers(American Institute of Physics, 2003-08-26) Thompson, GB; Banerjee, R; Fraser, HL; University System of Ohio; Ohio State University; University of Alabama TuscaloosaAs thin-film layers in a multilayered stack are reduced in thickness, changes in phase stability can result within the individual layers. These changes in phase are expected to have a significant influence upon the functional properties of the nanostructured composite. The ability to engineer, or tune, phase stability at this nanometer length scale is of significant importance in order to maximize the functional properties of these materials. We report the prediction and experimental conformation of tuning the hcp to bcc phase stability in Ti for Ti/Nb multilayered nanocomposites. The prediction was based upon selective alloying of Ti with a bcc beta stabilizing element using a new form of a thermodynamic phase diagram for predicting phase stability in thin-film multilayers. (C) 2003 American Institute of Physics.Item Predicting pseudomorphic phases in multilayers: Hexagonal-closed-packed Nb in Nb/Zr(American Institute of Physics, 2003-12-17) Thompson, GB; Banerjee, R; Fraser, HL; University of Alabama Tuscaloosa; University System of Ohio; Ohio State UniversityAs the dimensions of materials are reduced to the nanometer scale, changes in phase stability, referred to as pseudomorphism, are being reported. Such changes in phase stability are often serendipitously discovered in multilayered thin films. In this letter, we use a classical thermodynamic treatment to model and predict phase stability in Nb/Zr multilayers. An outcome of this letter is the development of a biphase stability diagram that represents the interrelationship of phase stability to volume fraction and length scale. Using this methodology, an hcp Nb phase stability field was empirically postulated and subsequently confirmed by x-ray and electron diffraction. The successful prediction of this phase, based upon classical thermodynamics quantities, suggests that other types of phase stabilities in other multilayers could be proposed using the biphase diagram. (C) 2004 American Institute of Physics.Item Size Effect Ordering in [FePt]100-xCrx Nanoparticles(2006-03-02) Thompson, G. B.; Srivastava, C.; Harrell, J. W.; Nikles, D. E.; University of Alabama TuscaloosaA series of [FePt]100−xCrx nanoparticles (x=5, 10, and 16at.%) was chemically synthesized by two different techniques. In one method, the simultaneous chemical reduction of FeCl2∙4H2O, Pt-acetylacetonate, and Cr-acetylacetonate was used with 2, 4 hexadecanediol as the reducing agent and phenyl ether as the solvent. The as-prepared particles had a mean size of 1.5nm. In the second method, the simultaneous chemical reduction of Pt-acetylacetonate and Cr-acetylacetonate and the thermal reduction of Fe(CO)5 were used with adamantanecarboxylic acid as the reducing agent and hexadecylamine as the solvent. These as-prepared particles were 3.5nm in size. X-ray diffraction confirmed that the Cr formed a solid solution within the A1 FePt phase for both processes. Upon annealing, the Cr hindered sintered grain growth of FePt nanoparticle arrays. Consequently, we were able to use Cr as a means to tune the ordering temperature as a function of the size effect in FePt nanoparticles. The presence of Cr in the ordered FePt reduced the magnetic coercivity of the transformed nanoparticles.Item Sintering behavior of spin-coated FePt and FePtAu nanoparticles(American Institute of Physics, 2006-04-19) Kang, SS; Jia, Z; Zoto, I; Reed, D; Nikles, DE; Harrell, JW; Thompson, G; Mankey, G; Krishnamurthy, VV; Porcar, L; University of Alabama Tuscaloosa; United States Department of Energy (DOE); Oak Ridge National Laboratory; National Institute of Standards & Technology (NIST) - USAFePt and [FePt](95)Au-5 nanoparticles with an average size of about 4 nm were chemically synthesized and spin coated onto silicon substrates. Samples were subsequently thermally annealed at temperatures ranging from 250 to 500 degrees C for 30 min. Three-dimensional structural characterization was carried out with small-angle neutron scattering (SANS) and small-angle x-ray diffraction (SAXRD) measurements. For both FePt and [FePt](95)Au-5 particles before annealing, SANS measurements gave an in-plane coherence length parameter a=7.3 nm, while SAXRD measurements gave a perpendicular coherence length parameter c=12.0 nm. The ratio of c/a is about 1.64, indicating the as-made particle array has a hexagonal close-packed superstructure. For both FePt and FePtAu nanoparticles, the diffraction peaks shifted to higher angles and broadened with increasing annealing temperature. This effect corresponds to a shrinking of the nanoparticle array, followed by agglomeration and sintering of the nanoparticles, resulting in the eventual loss of positional order with increasing annealing temperature. The effect is more pronounced for FePtAu than for FePt. Dynamic coercivity measurements show that the FePtAu nanoparticles have both higher intrinsic coercivity and higher switching volume at the same annealing temperature. These results are consistent with previous studies that show that additive Au both lowers the chemical ordering temperature and promotes sintering. (C) 2006 American Institute of Physics.Item In Situ Transmission Electron Microscopy of Ion Irradiated Fe-Pt Alloy Thin Films(2006-12-21) Thompson, G. B.; Morgan, N. W.; Birtcher, R. C.; University of Alabama TuscaloosaWe report the microstructural evolution during irradiation of FePt and FePt 25at.% thin films sputter deposited onto electron transparent silicon monoxide substrates. The films were studied in situ for 500keV Kr+ irradiation up to a fluence of 1015ions/cm2 or 4displacements∕atom (dpa). Upon irradiation to approximately 1dpa, the initial disconnected granular morphology became continuous. In particular, for FePt, accelerated grain growth was observed once the continuous morphology was achieved during ambient temperature irradiation. No atomistic (chemical) ordering from the as-deposited A1 phase into either the L10 FePt or L12 Fe3Pt phases was observed during ambient temperature irradiation. After irradiation, the specimens were then in situ annealed. The intermetallic ordering temperature, compared to that of an unirradiated film, was lowered by ≈200°C for FePt 25at.%. No decrease in the ordering temperature was observed for irradiated FePt. The rate of FePt grain growth during annealing was very similar for both irradiated and unirradiated films over the 25–650°C temperature range investigated.Item Microstructures and Magnetic Alignment of L10 FePt Nanoparticles(2007-05-09) Kang, Shishou; Shi, Shifan; Jia, Zhiyong; Thompson, G. B.; Nikles, David. E.; Harrell, J. W.; University of Alabama TuscaloosaChemically ordered FePt nanoparticles were obtained by high temperature annealing a mixture of FePt particles with NaCl. After the NaCl was removed with de-ionized water, the transformed FePt nanoparticles were redispersed in cyclohexanone. X-ray diffraction patterns clearly show the L10 phase. Scherrer analysis indicates that the average particle size is about 8 nm, which is close to the transmission electron microscopy TEM statistical results. The coercivity ranges from 16 kOe to more than 34 kOe from room temperature down to 10 K. High resolution TEM images reveal that most of the FePt particles were fully transformed into the L10 phase, except for a small fraction of particles which were partially chemically ordered. Nano-energy dispersive spectroscopy measurements on the individual particles show that the composition of the fully transformed particles is close to 50/ 50, while the composition of the partially transformed particles is far from equiatomic. TEM images and electron diffraction patterns indicate c-axis alignment for a monolayer of L10 FePt particles formed by drying a dilute dispersion on copper grids under a magnetic field. For thick samples dried under a magnetic field, the degree of easy axis alignment is not as high as predicted due to strong interactions between particles.Item Formation of FePt Nanoparticles by Organometallic Synthesis(2007-05-23) Bagaria, H. G.; Johnson, D. T.; Srivastava, C.; Thompson, G. B.; Shamsuzzoha, M.; Nikles, D. E.; University of Alabama TuscaloosaOur interest in determining the mechanism of FePt nanoparticle formation has led to this study of the evolution of particle size and composition during synthesis. FePt nanoparticles were prepared by the simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl. During the course of the reaction, samples were removed and the particle structure, size, and composition were determined using x-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy–energy dispersive x-ray spectrometry. Early in the reaction the particles were Pt rich (greater than 95at.% Pt) and as the reaction proceeded the Fe content increased to the target of 50%. The particle diameter increased from 3.1to4.6nm during the reaction. Energy dispersive x-ray spectrometry measurements of individual particle compositions using a high resolution TEM showed a broad distribution of particle compositions with a standard deviation greater than 15% of the average composition.Item Formation Mechanism and Composition Distribution of FePt Nanoparticles(2007-11-27) Srivastava, Chandan; Balasubramanian, Jayendra; Turner, C. Heath; Wiest, John M.; Bagaria, Hitesh G.; Thompson, Gregory B.; University of Alabama TuscaloosaSelf-assembled FePt nanoparticle arrays are candidate structures for ultrahigh density magnetic storage media. One of the factors limiting their application to this technology is particle-to-particle compositional variation. This variation will affect the A1 to L10 transformation as well as the magnetic properties of the nanoparticles. In the present study, an analysis is provided for the formation mechanism of these nanoparticles when synthesized by the superhydride reduction method. Additionally, a comparison is provided of the composition distributions of nanoparticles synthesized by the thermal decomposition of Fe(CO)5 and the reduction of FeCl2 by superhydride. The latter process produced a much narrower composition distribution. A thermodynamic analysis of the mechanism is described in terms of free energy perturbation Monte Carlo simulations.Item Selective Area Synthesis of Magnesium Oxide Nanowires(2007-11-28) Kim, G.; Martens, R. L.; Thompson, G. B.; Kim, B. C.; Gupta, A.; University of Alabama TuscaloosaSingle crystalline magnesium oxide MgO nanowires exhibiting a square cross section have been grown on 001-oriented MgO and Si substrates using the vapor-liquid-solid growth mechanism. While the nanowires grow vertically aligned on MgO, they display random orientations on the silicon substrate. For growth on MgO substrates, the selective placement and density of the nanowires can be controlled by using electron beam lithography for prepatterning the gold catalyst layer. The nanowire samples have been characterized using field-emission scanning electron microscopy and transmission electron microscopy. The described process for selective placement of the nanowires is attractive for their use as templates for coaxial coatings and also for their manipulation for potential device fabrication.Item Wetting of Al2O3 by molten aluminum: The influence of BaSO4 additions(Hindawi, 2008) Aguilar-Santillan, Joaquin; University of Alabama TuscaloosaThe effects of BaSO4 additions on the wetting of alumina by molten aluminum were studied by the sessile drop technique. To study the effect of BaSO4 decomposition (1100-1150 degrees C), the additions were treated at two temperatures 700 degrees C (973 K) and 1450 degrees C (1723 K), respectively. BaSO4 additions at low and high temperatures did not improve the nonwetting character of these compositions. However, at higher firing temperature, the formation of BA(6) (BaO center dot 6Al(2)O(3)) has a nonwetting trend with increasing its content. To address the BA(6) specifically a pure BaO center dot 6Al(2)O(3) was produced and tested. It was more nonwetting than the pure alumina. After the analysis of the contact angles for the BaSO4 and the BA(6) (BaO center dot 6Al(2)O(3)), it was concluded that these additions to alumina do not inhibit wetting by molten aluminum. In fact, at the addition levels common for refractories, the wetting tendency of molten aluminum is enhanced. Alternative explanations for the effectiveness of BaSO4 additions to alumina refractories are discussed. Copyright (C) 2008 Joaquin Aguilar-Santillan.Item Compositional Evolution During the Synthesis of FePt Nanoparticles(2008-09-25) Thompson, G. B.; Srivastava, Chandan; Nikles, David E.; University of Alabama TuscaloosaA series of FePt nanoparticles was synthesized by the thermal decomposition of iron pentacarbonyl and reduction in platinum acetylacetonate in phenyl ether solvent. A range of precursor molar ratios of 2, 1.5, and 1 between iron pentacarbonyl and platinum acetylacetonate was studied. After 30 min of reflux, the synthesis method produced a wide distribution in composition and size for the nanoparticles. Given 200 min of reflux, it was observed that the particle-to-particle composition and size narrowed, and the atomic ratio of Fe to Pt, for the majority of nanoparticles, approached the initial precursor molar ratios except for the molar ratio of 1. It is speculated that the compositional variability may be a result of the slow kinetics of iron pentacarbonyl’s decomposition in the reaction.Item Tailoring Nucleation and Growth Conditions for Narrow Compositional Distributions in Colloidal Synthesized FePt Nanoparticles(2008-11-21) Thompson, Gregory B.; Srivastava, Chandan; Nikles, David E.; University of Alabama TuscaloosaTo eliminate compositional and size variabilities between individual binary nanoparticles, it is essential to control the mechanistic steps involved in nanoparticle synthesis. A common method for synthesizing FePt nanoparticles involves the simultaneous decomposition and reduction in iron and platinum precursors, respectively. This simultaneous nucleation and growth method yields wide composition and size distributions. This paper describes and experimentally validates a methodology needed to tighten composition and size distributions for this process. By engineering the surfactant chemistry with tertiary phosphines to tightly bind the iron atoms in the iron precursor, uniform platinum rich seeds form during the initial stages of the synthesis. A thermodynamically preferred heterogeneous nucleation of iron atoms into these uniform platinum seeds in the subsequent stages produces a final dispersion with uniform particle-to-particle compositions. The paper addresses the understanding for optimizing the nucleation and growth sequences for compositional control in FePt nanoparticles.Item Designing, manufacturing, testing, and optimizing of micro-fuel cells(University of Alabama Libraries, 2009) Lu, Yuhao; Reddy, R. G.; University of Alabama TuscaloosaMicro-fuel cells are considered as promising electrochemical power sources in portable electronic devices. Performance of micro-fuel cells are closely related to many factors, such as processes of fabrication, designs of flow fields, and operating conditions. In the present research, micro-proton exchange membrane fuel cells (PEMFCs) and micro-direct methanol fuel cells (DMFCs) were systematically investigated from the aspects of structure design, bipolar/end plates (BPs) fabrication, and fuel cells evaluation. In chapter 3, compared with conventional machining and rapid prototyping (RP) technology, microelectromechanical system (MEMS) technology was the practicable method to fabricate the BPs with channels of a few microns width. Experimental and modeling methods were employed to analyze performance of the micro-PEMFC in chapter 4. Contact resistance changed significantly the distribution of overpotential in the micro-PEMFC and decreased the current output. Small dimensions of the micro-channel drastically affected the species transport and resulted in a non-uniform current distribution along channel direction at low cell potential (high current). In chapters 5, four kinds of flow fields, mixed multichannel serpentine with wide channels, single channel serpentine, double channel serpentine, and mixed multichannel serpentine with narrow channels, were applied to micro-PEMFCs. Results suggested that the micro-PEMFC with good performance should use the flow field with a mixed multichannel design and long micro-channels. In chapter 6, the same flow fields were studied in the micro-DMFCs. Concentration and flow rates of methanol solution affected performance of micro-DMFCs. A micro-DMFC with the long and narrow channels needed to take long time to reach the stable stage when an electric load on it was changed. In chapter 7, a passive air-breathing micro-DMFC with low loading of catalysts was developed. Performance of the passive micro-DMFC became poor with the increase in concentration of methanol solution. Power densities of the passive micro-DMFC drastically depended on the current scanning rate. Finally, cobalt phthalocyanine was introduced to platinum catalyst system to improve and optimize the micro-DMFCs. After heat-treatment at 635 oC, CoPc-Pt/C demonstrated good electrocatalytic activity for oxygen reduction reaction (ORR) and high methanol tolerance. However, CoPc-Pt/C heated at 980 oC showed a good electrocatalytic activity for MOR in DMFCs.Item L10 Ordering of FePt Thin Films using Sub-10 ms Laser Pulses(2009-03-12) Thompson, G. B.; Inaba, Y.; Kang, S.; Izatt, J. R.; Harrell, J. W.; Kubota, Y.; Klemmer, T. J.; University of Alabama TuscaloosaThe structural and magnetic properties of 10 nm FePt thin films annealed using a 1064 nm wavelength laser with 10, 7.5, 5.0, and 2.5 ms pulses have been examined. The A1 to L10 phase transformation was confirmed by x-ray diffraction (XRD). The maximum order parameter of 0.53 and coercivity of 5.36 kOe can be obtained with 10 ms pulse width laser annealing at a laser energy fluence of 10 J/cm2. The order parameter of the furnace annealed samples was approximately 1.0 suggesting that 10 ms is insufficient to obtain a fully ordered phase. The laser annealed grain size, as measured by in-plane XRD analysis, is 24 % smaller than that of furnace annealed sample for an equivalent order parameter demonstrating the merit of short time annealing.Item Magnetic, ferroelectric, and dielectric properties of Bi(Sc0.5Fe0.5)O-3-PbTiO3 thin films(American Institute of Physics, 2009-04-01) Yan, F.; Sterianou, I.; Miao, S.; Reaney, I. M.; Lai, M. O.; Lu, L.; National University of Singapore; University of Sheffield; University of Alabama TuscaloosaBi(Sc0.5Fe0.5)O-3-PbTiO3 (BSF-PT) thin films with a composition in the vicinity of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases have been grown on LaNiO3/SiO2/Si substrates at 550 degrees C and 150 mTorr by pulsed laser deposition. The dielectric properties of the film were enhanced due to high crystallinity, low porosity, and the vicinity of the MPB. A saturated ferroelectric hysteresis loop was obtained with 2P(r)=76 mu C/cm, and the leakage current was minimized by cooling the samples, postdeposition in O-2. Magnetic measurements revealed that BSF-PT thin films were antiferromagnetic confirming their anticipated multiferroic nature. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3093691]Item The effect of copper on the eutectoid transformation in ductile iron(University of Alabama Libraries, 2010) Samuel, Chris; Viswanathan, S.; University of Alabama TuscaloosaAs a result of the shortage in the availability of suitable steel scrap, trace elements are unintentionally added to ductile iron from the scrap available for melting. The effect of some of these trace elements on graphite shape, the resulting microstructure, and the dimensional behavior of the cast component are not well understood. The lack of control of these trace elements leads to excessive scrap as well as additional heat treatment costs, especially when ferritic or fully pearlitic microstructures are required. This work focuses on the effect of one element, copper, that occurs as a trace element or is often deliberately added when pearlitic microstructures are desired. Ductile iron samples with copper levels ranging from 0 to 0.8 wt. % were investigated. Gleeble dilatometry was used to characterize phase transformations and microstructure development. The diffusion coefficient of carbon in ferrite in the presence of copper and silicon was measured using multicomponent solid-solid diffusion experiments. Copper appears to have little or no effect on the diffusion coefficient of carbon in ferrite. Interrupted solidification experiments are used to explain solidification and segregation in ductile iron, and a revised model of ductile iron solidification is presented. It is shown that the segregation of copper during solidification is key to the pearlite promoting effect of copper and is related to the decrease in the driving force for the diffusion of carbon through the ferrite shell.Item Investigation of the effect of hafnium and chromium additions on the microstructures and short-term oxidation properties of DC magnetron sputtered β-nial bond coats deposited on Ni-based superalloys(University of Alabama Libraries, 2010) Bestor, Michael Alan; Weaver, Mark Lovell; University of Alabama TuscaloosaThermal barrier coatings play a major role in protecting turbine blades from extreme operating environments and extending service lifetimes. Reactive elements (e.g. Zr, Hf, Y, Si, etc.) have been shown to enhance the oxidation performance of such coating systems when added in appropriate amounts to overlay bond coats. This study investigated the influences of processing parameters along with Hf and Cr additions on the short-term oxidation performance of β-NiAl based coatings deposited via direct current magnetron sputtering onto CMSX-4 and René N5 substrates. Sputtering parameters were optimized to yield a zone T microstructure. The results indicate that the coatings are deposited as a solid solution and precipitation with the RE-doped coatings occur following annealing at 1000°C for times up to four hours. Precipitates form heterogeneously within the coatings with larger precipitates forming at grain boundaries and smaller ones forming within the grains at prior dislocation lines. Small incorporations of Cr into the NiAl-1Hf coating increased the average grain size and precipitate size. Transmission electron microscopy and atom probe tomography confirmed that the chemistry of the precipitates is mostly β'-Ni2AlHf accompanied by HfC and α-Cr. The results from the isothermal oxidation studies at 1050°C indicated that increasing the preoxidation annealing time from two to four hours decreased the mass gains observed with the specimens up to 100 hours. However, significant oxidation at the coating/substrate interface was discovered and the amount of oxidation increased with Hf content and preoxidation annealing time. This oxidation is thought to be caused by the large number of pinhole defects with the iii zone T microstructure and large grain boundary volume. Increased Hf concentrations were also found at the coating/substrate interface and this has been shown to lead to dramatic internal oxidation. The NiAlCrHf samples contain larger grain sizes and precipitates and a thinner TGO than the NiAl-Hf coatings. This combined with the lower mass gains during isothermal oxidation indicate that the NiAlCrHf coatings rapidly form a thin, protective α-Al2O3 layer that limits additional transport of oxygen to the bond coat. The results have been analyzed and discussed relative to previous research on sputter deposited NiAl-Hf coatings.Item Microstructural formations and phase transformation pathways in tantalum carbides(University of Alabama Libraries, 2010) Morris, Robert Allen; Thompson, Gregory B.; University of Alabama TuscaloosaTransition metal carbides have a large assortment of applications because of their high hardness, chemical resistance, and high melting temperatures. Tantalum carbide (TaC) and its sub-stoichiometric Ta2C and Ta4C3 phases have emerged as candidate materials for ultra-high temperature structural applications. A consequence of the high melting temperature is the limiting methods to fabricate near-net shape, near full density tantalum carbides. In general, hot-isostatic pressing (HIP) and/or arc melting/vacuum plasma spraying (VPS) of powders are the viable means of manufacturing. In HIP'ing, the phase formation is through solid-state reactions whereas arc melting/VPS involves rapid solidification. Additionally, the precipitation of multiple phases generates various orientation relationships that influence the grain morphology. Depending on carbon content, the grains were equiaxed, equiaxed with a cross-hatch pattern of thin laths of secondary phases, to acicular grains. The microstructures were quantified through a series of different 2D and 3D analytical techniques. To understand how these microstructures developed, a series of XTa:(1-X)C (0.5