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Browsing by Author "Turner, C. Heath"

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    Advanced solvents for CO2 separation applications
    (University of Alabama Libraries, 2016) Flowers, Brian Steven; Bara, J. E.; University of Alabama Tuscaloosa
    The objective of this dissertation is to advance the understanding of several novel solvents for CO2 capture and separation applications. Many of the solvents investigated were imidazole based, as these compounds are highly tunable, neutral, and less expensive analogs to imidazolium based ionic liquids (ILs). While much is known about the physical properties of ILs, the physical properties of these neutral compounds have not been researched as thoroughly, and so there is a need to explore these compounds as potential CO2 capture media. It has been further proven that the most effective means of predicting CO2 capture performance in imidazole based compounds is by examining the fractional free volume (FFV) using a molecular simulation program like COSMOTherm. Other non-imidazole based physical solvents were synthesized and compared to commercially available processes. 1,2,3-Trimethyoxypropane (1,2,3 TMP) was found to compare favorably with regard to CO2 absorption and viscosity to the current industry standard for CO2/CH4 pre-combustion separation techniques, Selexol, while being significantly less toxic. Chemical solvents for post-combustion CO2 capture were also investigated. It was determined that changing the substituents on 1-(3-aminopropyl)imidazole increases the CO2 solubility by increasing the basicity of the imidazole ring. The advantages in vapor pressure of these substituted aminopropylimidazole over traditionally used alkanolamines could potentially provide massive operational savings by reducing solvent losses through evaporation and increased solvent life.
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    Characterization of bismuth telluride two-dimensional nanosheets for thermoelectric applications
    (University of Alabama Libraries, 2015) Guo, Lingling; Wang, Hung-Ta; University of Alabama Tuscaloosa
    Solid-state thermoelectric devices are compact, scalable, quiet, and environmentally friendly, which are widely used as thermal engines or refrigerators. Bismuth telluride (Bi2Te3) and other V-VI group chalcogenides are known as one of the best thermoelectric materials specifically for applications in a temperature environment from room temperature to 300 ℃. Recently, the unique topological surface states were discovered in Bi2Te3 family materials, and these novel surface states are arisen from a strong spin-orbit coupling in topological insulators. Topological surface states are protected against time-reversal perturbations (i.e., non-magnetic impurities or surface defects), making the electronic transport essentially dissipation-less. Such unique transport behavior with zero energy loss provides new opportunities to enhance thermoelectric properties. Although the promise in thermoelectric properties of topological insulators have been shown in theoretical reports, there is a lack of experimental investigations for a better understanding of their basic properties. This research work focuses on the characterizations of fundamental properties of Bi2Te3 two-dimensional (2D) nanosheets. Samples were prepared via respective solvothermal synthesis and van der Waals epitaxy. The charged surface properties of Bi2Te3 2D nanosheets were investigated using kelvin probe force microscopy. The measured electrical potential difference between aminosilane self-assembled monolayer and Bi2Te3 nanosheet surfaces is found to be ∼650 mV, which is larger than that (∼400 mV) between the silicon oxide substrate and Bi2Te3 nanosheet surface. The elastic properties of Bi2Te3 2D nanosheets (i.e., Young’s modulus and prestress) were acquired by analyzing the thickness dependence of 2D nanosheet deformations creating by atomic force microscopy tips. The Young's modulus by fitting linear elastic behaviors of 26 samples is found only 11.7–25.7 GPa, significantly smaller than the bulk in-plane Young's modulus (50–55 GPa). Furthermore, the thermoelectric properties of Bi2Te3 2D nanosheets were characterized in the cryostat system at a temperature range of 20-400 K. The results reveal that electrical conductivity of 2D nanosheets decreases with increasing temperature and thickness, while the measured Seebeck coefficient does not show a strong thickness dependence and the value is smaller than bulk Bi2Te3. These fundamental properties would help improve the basic understanding of topological surface states towards practical applications.
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    Computational studies of the fundamental thermodynamic properties of amino acids and small peptides
    (University of Alabama Libraries, 2015) Stover, Michele Leigh; Dixon, David A.; University of Alabama Tuscaloosa
    In 2011, the Human Proteome Project (HPP) was launched with the main goal of experimentally mapping the entire human proteome. Determining a protein’s sequence is a first step to understanding its structure and function, which are of great importance in biological, biochemical, and medical studies. The sequencing of peptides and proteins by mass spectrometry (MS) has become a major tool in proteomics research because it is a cost effective and highly reproducible analytical technique. The analysis of biomolecules by mass spectrometry requires an understanding of proton transfer reactions because the two most commonly used ionization techniques, electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI), involve the addition and removal of protons. The sites of proton transfer reactions can affect the fragmentation patterns of peptide ions, which consequently impacts the sequence information that can be obtained from mass spectrometry experiments. Thermodynamic values, such as the gas-phase acidity (GA or ∆Gacid), the ΔG for the deprotonation reaction AH → A- + H+, provide valuable information to help in understanding the less studied negative ion peptide fragmentation mode by mass spectrometry. The study of gas-phase proton transfer reactions provides unique insights into the structures and energetics of the peptides. Changing the protonation state can impact the hydrogen bonding in the molecule and result in decreased or increased properties such as solubility, hydrophobicity, and electrostatic interactions. By combining these experimentally obtained results with the results from high level electronic structure theory calculations, an improved understanding of the structures and energetics of polypeptides can be obtained. Herein we describe computational studies using reliable, correlated molecular orbital methods of the gas-phase properties, including acidities and heats of formation, and solution-phase acidities of amino acids (AAs) and small peptides including substituted molecules such as AA amides and phosphorylated AAs. This dissertation will focus on the prediction of fundamental thermodynamic properties of AAs and small peptides that are of interest in the area of biochemistry, proteomics, and the Human Proteome Project.
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    Computational studies of transition metal catalysts
    (University of Alabama Libraries, 2010) Craciun, Raluca; Dixon, David A.; University of Alabama Tuscaloosa
    High level electronic structure calculations were used to evaluate reliable, self-consistent thermochemical data sets for the second and third row transition metal hexafluorides, as well as for metal phosphines (M=Ni, Pd, Pt). For the transition metal hexafluorides, the electron affinities, heats of formation, first (MF₆ → MF₅ + F) and average M-F bond dissociation energies, and fluoride affinities of MF₆ (MF₆ + F⁻ → MF₇⁻) and MF₅ (MF₅ + F⁻ → MF₆⁻) were calculated. For the transition metal phosphines, the first metal-phosphine binding energy in MPH₃, M(PH₃)₂, MPH₃Cl₂ and M(PH₃)₂Cl₂ was calculated. The electron affinities, which are a direct measure for the oxidizer strength, increase monotonically in the second and third row series, from WF₆ to AuF₆, and from MoF₆ to AgF₆. The hexafluorides of the last two elements of each series, Pt, Au in the third row and Pd and Ag in the second, form extremely powerful oxidizers. The inclusion of spin orbit corrections is necessary to obtain the correct qualitative order for the electron affinities. The calculated electron affinities increase with increasing atomic number, are in good agreement with the available experimental values and, for the third row are: WF₆ (3.15 eV), ReF₆ (4.58 eV), OsF₆ (5.92 eV), IrF₆ (5.99 eV), PtF₆ (7.09 eV), and AuF₆ (8.20 eV). The electron affinities of the second row hexafluorides are even larger than for the second row: MoF₆ (4.23 eV), TcF₆ (5.89 eV), RuF₆ (7.01 eV), RhF₆ (6.80 eV), PdF₆ (7.95 eV), AgF₆ (8.89 eV). A wide range of density functional theory exchange-correlation functionals were also evaluated and only three gave satisfactory results as compared to the higher level electronic structure calculations. The corresponding pentafluorides are extremely strong Lewis acids. The optimized geometries of the corresponding MF₇⁻ anions show classical structures with M-F bonds for W through Ir and for Mo, Tc and Rh; however, for PtF₇⁻, AuF₇⁻, RuF₇⁻, PdF₇⁻, and AgF₇⁻ nonclassical anions were found with a very weak external F-F bond between an MF₆⁻ fragment and a fluorine atom. These anions are text book examples for "superhalogens" and can serve as F atom sources under very mild conditions.
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    The computational studies on the chemistry of titanium dioxide nanoparticles
    (University of Alabama Libraries, 2010) Wang, Tsang-Hsiu; Dixon, David A.; University of Alabama Tuscaloosa
    The chemistry of TiO_2 and SiO_2 nanoclusters is studied using computational methods. The potential energy surfaces (PESs), thermochemistry of the intermediates, and the reaction paths for the initial steps of the hydrolysis of TiCl_4 were calculated. Transition state theory and RRKM unimolecular rate theory are used to predict the rate constants. Clustering energies and heats of formation are calculated for neutral clusters, and the calculated heats of formation were used to study condensation reactions. The reaction energy is substantially endothermic if more than 2 HCl are eliminated. The calculations show that the reported values for ΔH_f^0(TiOCl_2) should be remeasured. Transition metal oxides such as TiO_2 can be used as photocatalysts to control chemical transformations for energy production. An important applications for TiO_2 is its use to photochemically split water to produce H_2 and O_2. The PES for splitting water on the ground and first excited state surfaces of (TiO_2)_n (n=1-4) nanoparticles have been studied up through the coupled cluster CCSD(T)/complete basis set level. Water is readily split to form hydroxyl groups without the need for a photon. Experimental measurements of the photoconversion of ketones (C(O)RR') on the rutile TiO_2 (110) surface show that one can eliminate R or R'. The bond dissociation energies of R=CH_3 and a wide range of R' for the gem-diols CRR'(OH)_2 were calculated at the density functional theory (DFT) and G3(MP2) levels. The calculated bond dissociation energies are in excellent agreement with the experimental values. The calculations show that most of the photodissociation processes are under thermodynamic control except for R'=CF_3. X-ray photoelectron spectroscopy (XPS) and DFT electronic structure calculations were used to study the average formal oxidation state of silicon in fumed silica (CAB-O-SIL®). The results show that the average surface oxidation state of the silicon in fumed silica is predominantly +1 and suggest a notably less hydrophilic character for CAB-O-SIL® than the oxides of silicon with Si in the formal +3 and +4 oxidation states. Once the +3 oxidation state is formed, water on the silica surface facilitates the conversion of the Si^+3 to the Si^+4 oxidation state.
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    Computational Study of Thermodynamics of Metal Carbonates and Catalytic Properties of Group IV Transition Metal Oxides
    (University of Alabama Libraries, 2023) Hu, Yiqin; Dixon, David A.
    This dissertation describes computational studies of the thermodynamics of metal carbonates, the sequestration of CO2 by group IV transition metal oxides, the reactivity of ethanol on group IV transition metal oxides as a model for biofuel conversion, and halogen atom oxidation of magnesium clusters. Gas phase heats of formation using the Feller-Peterson-Dixon (FPD) approach were predicted for carbonates, bicarbonates and hydroxides for Mg, Ca, and various first-row transition metals. These reliable FPD values were used to benchmark a range of density functional theory exchange-correlation functionals that are used in modeling larger systems and solids. None of the functionals show good chemical accuracy of ±1 kcal/mol, most likely due to issues with properly treating oxygen. The FPD results can be used to predict cohesive energies and metal atom exchange reactions. The addition of CO2 to M3O6 and M3O6- was studied at the CCSD(T) using weighted core correlation consistent basis sets. The calculations showed that prior predictions on the Ti structures were not correct as the results require the use of weighted core functions. The calculations enabled comparisons of CO2 binding energies to the neutral and anionic clusters as well the role that CO2 binding has on the electron affinity of the cluster. Ethanol dehydration and dehydrogenation on (TiO2)n nanoclusters, n = 2 to 4, which serve as models for the bulk TiO2 surface were studied at the CCSD(T)/aD//B3LYP/DZVP2 level to provide insights into how metal oxides can be used to convert biofuel into fuels or feedstocks for the chemical industry. The Lewis/Brønsted acidity and basicity on the Ti and O sites were correlated with various energetics. The oxidation of small Mg clusters by F and Cl was studied to interpret the observed chemiluminescence. The computational results provide the best available energetics for these species and are critical to interpreting the experiments which date back more than 40 years.
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    Confinement Effects on Carbon Dioxide Methanation: A Novel Mechanism for Abiotic Methane Formation
    (Nature Portfolio, 2017) Le, Thu; Striolo, Alberto; Turner, C. Heath; Cole, David R.; University of London; University College London; University of Alabama Tuscaloosa; Ohio State University
    An important scientific debate focuses on the possibility of abiotic synthesis of hydrocarbons during oceanic crust-seawater interactions. While on-site measurements near hydrothermal vents support this possibility, laboratory studies have provided data that are in some cases contradictory. At conditions relevant for sub-surface environments it has been shown that classic thermodynamics favour the production of CO2 from CH4, while abiotic methane synthesis would require the opposite. However, confinement effects are known to alter reaction equilibria. This report shows that indeed thermodynamic equilibrium can be shifted towards methane production, suggesting that thermal hydrocarbon synthesis near hydrothermal vents and deeper in the magma-hydrothermal system is possible. We report reactive ensemble Monte Carlo simulations for the CO2 methanation reaction. We compare the predicted equilibrium composition in the bulk gaseous phase to that expected in the presence of confinement. In the bulk phase we obtain excellent agreement with classic thermodynamic expectations. When the reactants can exchange between bulk and a confined phase our results show strong dependency of the reaction equilibrium conversions, XCO2, on nanopore size, nanopore chemistry, and nanopore morphology. Some physical conditions that could shift significantly the equilibrium composition of the reactive system with respect to bulk observations are discussed.
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    The Density and Molecular Phase Field Methods
    (University of Alabama Libraries, 2022) Jacobson, David Wallace; Thompson, Gregory B.; University of Alabama Tuscaloosa
    Density phase field (DPF) methods have arisen as a means of more closely linking free energy functionals with grain boundary physics as opposed to using functionals that are purely phenomenological. In their current form, DPF methods exhibit a number of theoretical and computational problems that limit their applicability. These issues include the following:(1) being unable to simulate moving grain boundaries, (2) low computational performance due to high order gradient energy terms, and (3) failing to predict stable bulk equilibriums. We solve the mobility and performance issues mentioned above by coupling the density field of DPF simulations with traditional order parameters. The stable equilibrium problem is solved through the development of a criteria list that can be used to determine the set of DPF free energy functionals that correctly predict bulk equilibrium states. A subset of the free energy functionals that meet aforementioned criteria were identified and studied further because of their direct connection with atomistic physics. Termed the Molecular Phase Field (MoPF) method, these free energy functionals are constructed from interatomic potentials. Grain boundaries simulated using the MoPF method are material specific and their calculated excess energies are a natural consequence of the interatomic potential parameters used as model inputs. Lennard Jones, M-N, Mie, and Morse potential parameters have been calculated for over 30 different transition metals such that MoPF simulations of these metals may be carried out. Finally, MoPF models allow for the thermodynamic description of specific grain boundaries to be incorporated within phase field models such that the large variation in properties over the grain boundary phase space might be more accurately represented in phase field simulations.
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    Design and synthesis of phosphine ligands for palladium-catalyzed coupling reactions
    (University of Alabama Libraries, 2009) Brown, William Scott; Shaughnessy, Kevin H.; University of Alabama Tuscaloosa
    The synthesis and design of new phosphines is a continuing area of interest. In designing new phosphines there are a number of design features that need be considered. For palladium catalyzed coupling reactions, sterically demanding and electron releasing ligands are generally most effective in promoting the reaction. In evaluating the hydrophobic phosphines utilized in the Suzuki coupling, the neopentyl derivatives of TTBP (tri-tert-butylphosphine) were investigated. The effect of the addition of a neopentyl group increases the cone angle and impacts the electron donation by decreasing it relative to TTBP. The application in Suzuki coupling shows that a palladium catalyst with a neopentyl phosphine ligand demonstrates good to excellent yields with aryl bromides at room temperature. In the design of new phosphines, building in polar groups generates the ability to take advantage of using water as a solvent or co-solvent. The synthesis of the water soluble ligands DTBPPS (di-tert-butylphosphoniumpropane sulfonate) and DAPPS (di-adamantylphosphoniumpropane sulfonate) led to their testing in Sonogashira and Suzuki coupling reactions. Both ligands give catalysts that show good to excellent conversion of aryl bromides to products at room temperature. For aryl chlorides elevated temperatures are required. In expanding the water-soluble ligands into other palladium coupling reactions, DAPPS was developed in the carbonylation of aryl bromides. The palladium/DAPPS-catalyzed carbonylation coupling reactions show good to excellent conversion of aryl bromides to carbonylated products. This is the first example of a water-soluble alkylphosphine promoting carbonylation of an aryl bromide.
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    Development and applications in computational chemistry for inorganic catalysis
    (University of Alabama Libraries, 2013) Chen, Mingyang; Dixon, David A.; University of Alabama Tuscaloosa
    A robust metadata database called the Collaborative Chemistry Database Tool (CCDBT) for massive amounts of computational chemistry raw data has been designed and implemented. It performs data synchronization and simultaneously extracts the meta data. The indexed meta data can be used for data analysis and data mining. A novel tree growth - hybrid genetic algorithm (TG-HGA) was developed to search the global minimum of small clusters. In the TG algorithm, the clusters grow from a small seed to the size of interest stepwise. New atoms are added to the smaller cluster from the previous step, by analogy to new leaves grown by a tree. The initial structures for the search for the global minimum of TiO_2 nanoclusters were generated by TG-HGA, and new low energy structures that have not been previously reported were found. Low energy isomers of Agn, n = 2 - 99, were studied at different computational level depending on the size of Agn. The geometries of Agn, n = 2 - 8, were optimized using density functional theory (DFT), and the energies were calculated at the CCSD(T)/CBS level. The Agn, n = 9 - 20, were initially generated by the TG-HGA builder with an EAM potential, and optimized using the DFT method. The relative energies and normalized atomization energies for the optimized structures were calculated at the CCSD(T) level with a small basis set. For larger Agn, 20 < n < 100, the low energy structures were generated using TG-HGA with an EAM potential, and the energies were calculated at the DFT level with a small basis set. A range of DFT functionals were benchmarked with the normalized atomization energies at the CCSD(T) level for the small Agn clusters. PW91 and ω-B97XD provided best results for predicting the normalized atomization energies. The normalized atomization energies for Agn start to converge slowly to the bulk at n = 55. At n = 99, the normalized atomization energy is predicted to be ~50 kcal/mol. The low energy isomers of the Irn(CO)m complexes (n=1, 2, 3, 4, and 6) were investigated using electronic structure methods at the density functional theory and coupled cluster (CCSD(T) theory levels. Ir4(CO)12 is predicted to be the most favored complex for reactions of Irn(CO)m with CO at low temperature, and Ir6(CO)16 is predicted to be formed above room temperature. Smaller Irn(CO)m clusters will nucleate to form Ir4(CO)12 spontaneously. Low-lying structures of the small iridum clusters Irn (n = 2 - 8) were optimized using DFT methods. Ir2 and Ir3 were also optimized using the CASSCF method. MRCI-SD (for Ir2) energies and CCSD(T) (for Ir2 and Ir3) energies of the leading configurations from the CASSCF calculations were done to predict the low-lying states. The normalized atomization energies for Irn (n = 2 - 8) were calculated at the CCSD(T) level up to the complete basis set (CBS) limit in some cases using the B3LYP optimized geometries. Inclusion of the spin orbit corrections in the normalized atomization energies for Irn is critical and will decrease the normalized atomization energies by ~ 15 kcal/mol for n ≥ 4. Several molecular models were used to characterize various binding sites of the metal complexes in the zeolites. The calculated structures and energies indicate a metal-oxygen (M(I)-O) coordination number of two for most of the supported complexes but a value of three when the ligands include C2H5 or H. The results characterizing various isomers of supported metal complexes incorporating hydrocarbon ligands indicate that some carbene and carbyne ligands could form. A set of ligand bond dissociation energies is reported to explain reactivity trends. The Pd-L ligand bond dissociation energies (BDEs) of cis- and trans-[L-Pd(PH3)2Cl]+ were predicted using coupled cluster CCSD(T) theory and a variety of density functional theory (DFT) functionals at the B3LYP optimized geometries. For cis-[L-Pd (PH3)2Cl]+ complexes, the Pd-L bond energies are 28 kcal/mol for CO; ~40 kcal/mol for AH3 (A = N, P, As, and Sb), norbornene, and CH3CN; and ~53 kcal/mol for CH3NC, pyrazole, pyridine, and tetrahydrothiophene at the CCSD(T) level. The benchmarks show that the dispersion-corrected hybrid, generalized gradient approximation, DFT functional ω-B97X-D is the best functional to use for this system. Use of the ω-B97X-D/aD functional gives predicted BDEs within 1 kcal/mol of the CCSD(T)/aug-cc-pVTZ BDEs for cis-[L-Pd(PH3)2Cl]+ and 1.5 kcal/mol for trans-[L-Pd(PH3)2Cl]+ . Lanthanide metal atoms, produced by laser ablation, were condensed with CH3F in excess Ar at 8 K. New infrared absorption bands are assigned to the first insertion CH3LnF and oxidative addition methylene lanthanide hydride fluoride CH2LnHF products on the basis of 13C and deuterium substitution and density functional theory calculations of the vibrational frequencies. For Ln = Eu and Yb only CH3LnF is observed. CH3LnF in the Ln formal +2 state is predicted to be more stable than CH2LnHF with the Ln in the formal +3 oxidation state. CH3-LnF forms a single bond between Ln and C and is a substituted methane. The calculated potential energy surface for the CH3F + La → CH3-LaF/CH2-LaHF shows a number of intermediates and transition states on multiple paths. The reaction mechanism involves the potential formation of LaF and LaHF intermediates.
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    Engineering Patterned Nanofiltration Membranes and Amine-Based Solvents for Improved Industrial Wastewater Treatment
    (University of Alabama Libraries, 2025) Ward, Lauren; Weinman, Steven T.
    Produced water from the oil and gas industry contains high levels of salt, oils, and other components that are difficult to separate. Oil is particularly challenging to remove because it is emulsified into the water. Polymeric membranes can help remove this oil; however, membrane fouling is one of the biggest challenges with membrane processes. Fouling decreases the permeance and rejection of the membrane and decreases the lifetime of the membrane due to the harsh chemical cleaning required to remove the fouling. Adding surface patterns to membranes decreases fouling by creating areas of localized mixing. To understand the relationship between fouling and patterns sizes, we investigated oil droplet sizes of ~10 μm with patterns smaller than (300-nm), equal to (10-μm), and larger than (50-μm) the droplet size. The commercial, flat, and three patterned membranes were tested with water, sodium sulfate, and simulated oil solutions. We found that the larger than and smaller than patterns decreased the fouling rate more than the others. Hypersaline brines, such as reverse osmosis (RO) concentrate, contain high levels of total dissolved solids. Since this water is typically three times saltier than seawater, RO and distillation do not work or are very energy intensive. Therefore, a new method is needed to treat these hypersaline brines. Temperature swing solvent (TSSE) extraction utilizes a solvent’s ability to absorb and desorb water at different temperatures. Water will selectivity solubilize into an immiscible organic solvent at one temperature and this water will phase separate from the solvent at another temperature. Currently, there are two best-performing solvents, diisopropylamine (DIPA) and dipropylamine (DPA); however, a further polishing step is necessary because of high levels of solvent in the final product water. This work investigated constitutional isomer six-carbon amine-based solvents to understand what aspects of the molecular configuration allow DIPA and DPA to be the leading TSSE solvents. Our results show the symmetry and branching of DIPA and DPA are important driving factors in their desalination abilities. Finding a solvent that can reject high levels of salt, with high water production and little to no solvent crossover would help many industries.
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    Enhanced oil recovery simulation study for Citronelle field, Alabama
    (University of Alabama Libraries, 2012) Cox, William Brannon; Carlson, Eric S.; University of Alabama Tuscaloosa
    The world is on the verge of an energy crisis due to rising demand for fossil fuel to meet both domestic and industrial energy requirements. In order to meet this rising fossil fuel need, it is important that enhanced oil recovery (EOR) schemes, which are more efficient hydrocarbon recovery techniques than primary and secondary recovery methods, are used to recover conventional oil reserves from already discovered fields. Continuous CO2 and the Water Alternating Gas (WAG) injection schemes are two basic EOR techniques for gasflooding reservoirs. The primary objective of this research project focuses on enhancing oil recovery from a very small pilot area of Citronelle oil field using CO2 miscible flooding. The miscible flood performance of carefully targeted CO2 injection was modeled using a fine-scale open source compositional simulator nSpyres. The simulation runs were performed using regular grids with a total of 8.2 million cells. The CO2 injection pilot did not result in any new recovery. However, it helped identify many crucial characteristics for consideration in a comprehensive CO2 project for entire Citronelle field, such as non-workability of WAG scheme due to loss of injectivity after converting back to water injection, presence of natural and induced fractures that affects flood performance, as well as operational issues - down-hole pumps, well integrity, and difficulties with data collection due to the mixing of "power oil" with produced oil - which will need thorough consideration.
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    Enhancing the pre-polymerization coordination of 1-vinylimidazole in bulk solution with ionic liquid additions
    (University of Alabama Libraries, 2015) Hamilton, Jackie Ryan; Turner, C. Heath; University of Alabama Tuscaloosa
    Recent experimental investigations have found that the photopolymerization of 1-vinylimidazole (VIm) can be significantly accelerated with the addition of lithium bis(trifluoromethylsulfonyl)-imide (LiTf2N). However, a clear explanation for this phenomenon is lacking, and the underlying molecular level interactions in such a system are unknown. The two components, VIm and LiTf2N, are soluble over a wide range of concentrations at ambient temperature, and if the fundamental behavior of this mixture can be clearly quantified, there are significant opportunities for tuning the polymerization dynamics, polymer structure, and properties. In this work, molecular dynamics simulations are used to model the underlying pre-polymerization structure of VIm/LiTf2N mixtures at several different concentrations. It is found that the Li+ enhances the site-site interactions of key sites involved in the polymerization, and this is suggested to play a major role in the experimentally-observed enhancement of the polymerization behavior.
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    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 Tuscaloosa
    Self-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.
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    Hafnium alkylamides and alkoxide adsorption and reaction on hydrogen terminated silicon surfaces in a flow reactor
    (University of Alabama Libraries, 2010) Li, Kejing; Klein, Tonya M.; University of Alabama Tuscaloosa
    This work is a study of the gas phase and surface chemistry of three metalorganic Hf (IVB) precursors - tetrakis(dimethylamido)hafnium (TDMAH), tetrakis(ethylmethylamido)hafnium (TEMAH), and hafnium tert-butoxide (HTB) adsorption and reaction onto hydrogen terminated Si(100), Si(111) and Ge surfaces during low pressure chemical vapor deposition (CVD) in a temperature range of 25 ºC to 300 ºC in a flow reactor. The main methods used include in-situ attenuated total reflectance Fourier transforms infrared spectroscopy (ATR-FTIR), transmission IR, quadrupole mass spectrometer (Q-MS), ab inito density functional theory (DFT), photoelectron spectroscopy (XPS), finite element analysis (FEA), computational fluid dynamics (CFD), and atomic force microscopy (AFM). Possible gas phase decomposition and surface adsorption reactions were surveyed. Reaction energies, vibrational spectra and transition states were calculated for the three precursors and especially the two alkylamido hafnium precursors to support experimental observations. Interfacial bonding and surface catalyzed reaction processes initiated by the adsorption of precursors were detected. For TDMAH and TEMAH, β-hydride elimination and insertion reactions were calculated to be not favorable thermodynamically at these low experimental temperatures. Interfacial bonding during adsorption between the Si was through N-Si and/or C-Si. Decomposition products containing Hf-H species were observed on the surface at room temperature and 100 ºC and the peak assignment was confirmed by deuterated water experiments. The gas phase by-products were mostly dimethylamine (DMA) and a small amount of methylmethleneimine (MMI) or ethylmethylamine (EMA) and methylethyleneimine (MEI). A surface three-member cyclo species was tentatively identified. For HTB, interfacial bonding was Si-O or Ge-O. Another β-hydride elimination generated Hf-OH on the surface and t-butene in the gas phase. A monodentate and bidentate model was proposed for chemisorption of HTB with different concentration on two Si surface orientations at temperatures below 150 ºC. Carbonate was found to form in the film at higher temperatures. The effect of HTB buoyancy driven flow in the ATR flow through cell on thin film topography was observed using AFM of thin films deposited from HTB at 250 ºC. The images showed a wavy surface at the downstream end of the substrate due to roll-type flow predicted by CFD calculations.
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    In-situ investigation and mitigation of carbon support corrosion of cathode catalyst in PEM fuel cells
    (University of Alabama Libraries, 2010) Li, Wei; Lane, Alan M.; University of Alabama Tuscaloosa
    Carbon support corrosion (CSC) is one of the key factors causing cathode electrocatalyst (Pt/C) degradation in proton exchange membrane fuel cells (PEMFC). It is electrochemical oxidation and thus needs to be investigated in-situ with potential imposed. CSC was characterized in-situ and correlated to the Pt redox reactions and Pt-catalyzed oxygen reduction reaction (ORR) by the differential electrochemical mass spectrometry (DEMS) spectra of cathode exhaust gases, CO₂, H₂ and O₂, from a PEMFC fed with humidified H₂ and He to the anode and cathode respectively. Furthermore, the catalytic effects on CSC from different oxidation states of Pt were indicated. To determine the oxygen sources and pathways of CSC, oxygen was isotopically labeled by replacing regular water with oxygen-18 (¹⁸O) enriched water (H₂¹⁸O, 98%) in DEMS, denoted as ¹⁸O-DEMS. 18O-DEMS spectra of the cathode exhaust gases O₂, O¹⁸O, ¹⁸O₂, CO₂, CO¹⁸O and C¹⁸O₂ during cyclic voltammetry and chronoamperometry were analyzed to verify that water is the main direct oxygen source for CSC. Moreover, water reacts with carbon to produce at least three types of carbon surface oxides, which are further electrochemically oxidized with water to produce CO₂ in different potential ranges. After accelerated testing of cathode catalyst degradation in PEMFC using potential cycling between 100-1400 mV at the rate of 400 mV/s, the changes of mass spectra of CO₂, H₂ and O₂ over time showed that the CSC decreases as Pt electrochemically active surface area (ECSA) decreases, i.e. catalyst activity decreases, but the membrane does not degrade significantly in gas permeability. A hypothesis is proposed here that Au nanoparticles (NPs) added to a carbon-supported Pt (Pt/C) catalyst can mitigate the Pt catalytic effects on CSC by suppressing the Pt oxidation. Several methods were tried to synthesize Pt/C (20 wt% Pt) and bimetallic AuPt/C (20 wt% Pt, 5 wt% Au) catalysts including deposition-precipitation, two phase liquid-liquid colloidal, polyol, microwave-assisted polyol, and surface redox methods. TEM pictures showed that the EG method (polyol method using ethylene glycol), microwave-assisted EG method, and colloidal method produced Pt/C catalysts with high dispersion and narrow particle size distribution of Pt NPs uniformly loaded on the carbon support. Au NPs with high dispersion and narrow particle size distribution can be made only by the colloidal method. AuPt/C catalysts were synthesized by two methods: physically by mixing Au NPs prepared by the colloidal method on Pt/C prepared by the EG method, and chemically by surface redox reactions of a Au precursor on Pt NPs prepared by the EG method and then loaded on the carbon support (denoted as AuPtC-EG-SR). The existence of Au on Pt/C was confirmed by EDX and by a larger ring current from ORR experiment using a rotating ring-disk electrode. Three membrane electrode assemblies (MEA) with commercial Etek Pt/C and those two types of AuPt/C catalysts as cathode catalyst respectively were fabricated for CSC comparison. Larger ECSA but less CO₂ intensity of the MEA with a AuPtC-EG-SR cathode than those of the MEA with Etek Pt/C gives preliminary confirmation of the hypothesis.
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    Mathematical modeling of solidification phenomena in electromagnetically stirred melts
    (University of Alabama Libraries, 2014) Poole, Gregory Michael; Nastac, Laurentiu; University of Alabama Tuscaloosa
    A methodology is presented to simulate the electromagnetic, heat transfer, and fluid flow phenomena for two dimensional electromagnetic solidification processes. For computation of the electromagnetic field, the model utilizes the mutual inductance technique to limit the solution domain to the molten metal and magnetic shields, commonly present in solidification systems. The temperature and velocity fields were solved using the control volume method in the metal domain. The developed model employs a two domain formulation for the mushy zone. Mathematical formulations are presented for turbulent flow in the bulk liquid and the suspended particle region, along with rheological behavior. An expression has been developed--for the first time--to describe damping of the flow in the suspended particle region as a result of the interactions between the particles and the turbulent eddies. The flow in the fixed particle region is described using Darcy's law. Calculations were carried out for globular and dendritic solidification morphologies of an electromagnetically-stirred melt in a bottom-chill mold. The coherency solid fraction for the globular solidification morphology was taken to be 0.5, while the coherency for dendritic morphology was 0.25. The results showed the flow intensity in the suspended particle region was reduced by an order of magnitude. The effect of the heat extraction rate on solidification time was investigated using three different heat transfer coefficients. The results showed that the decrease in solidification time is nonlinear with respect to increasing heat transfer coefficient. The influence of the final grain size on the damping of the flow in the suspended particle region was examined, and it was found that larger grain sizes reduce the extent of flow damping.
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    Matilda: a mass filtered nanocluster source
    (University of Alabama Libraries, 2009) Kwon, GiHan; Klein, Tonya M.; University of Alabama Tuscaloosa
    Cluster science provides a good model system for the study of the size dependence of electronic properties, chemical reactivity, as well as magnetic properties of materials. One of the main interests in cluster science is the nanoscale understanding of chemical reactions and selectivity in catalysis. Therefore, a new cluster system was constructed to study catalysts for applications in renewable energy. Matilda, a nanocluster source, consists of a cluster source and a Retarding Field Analyzer (RFA). A moveable AJA A310 Series 1"-diameter magnetron sputtering gun enclosed in a water cooled aggregation tube served as the cluster source. A silver coin was used for the sputtering target. The sputtering pressure in the aggregation tube was controlled, ranging from 0.07 to 1torr, using a mass flow controller. The mean cluster size was found to be a function of relative partial pressure (He/Ar), sputtering power, and aggregation length. The kinetic energy distribution of ionized clusters was measured with the RFA. The maximum ion energy distribution was 2.9 eV/atom at a zero pressure ratio. At high Ar flow rates, the mean cluster size was 20 ~ 80nm, and at a 9.5 partial pressure ratio, the mean cluster size was reduced to 1.6nm. Our results showed that the He gas pressure can be optimized to reduce the cluster size variations. Results from SIMION, which is an electron optics simulation package, supported the basic function of an RFA, a three-element lens and the magnetic sector mass filter. These simulated results agreed with experimental data. For the size selection experiment, the channeltron electron multiplier collected ionized cluster signal at different positions during Ag deposition on a TEM grid for four and half hours. The cluster signal was high at the position for neutral clusters, which was not bent by a magnetic field, and the signal decreased rapidly far away from the neutral cluster region. For cluster separation according to mass to charge ratio in a magnetic sector mass filter, the ion energy of the cluster and its distribution must be precisely controlled by acceleration or deceleration. To verify the size separation, a high resolution microscope was required. Matilda provided narrow particle sized distribution from atomic scale to 4nm in size with different pressure ratio without additional mass filter. It is very economical way to produce relatively narrow particle size distribution.
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    Microchemical systems for understanding of multiphase flows in upstream hydrocarbon and natural gas productions
    (University of Alabama Libraries, 2015) Hu, Chuntian; Hartman, Ryan L.; University of Alabama Tuscaloosa
    This dissertation focuses on the design and the application of microchemical systems to understand multiphase flows in upstream hydrocarbon and natural gas productions. Offshore petroleum and natural gas catastrophes, such as the Deepwater Horizon spill of 2010, motivate the need to understand how to minimize the introduction of potentially invasive compounds while maximizing their efficacy during emergency remediation. The microfluidic stabilities of mineral oil-seawater multiphase flows in the presence of model dispersants were studied for We < 1. Introducing dispersants at varying dimensionless volumetric injection rates, ranging from 0.001 to 0.01, transitions from stable slug flow to the bubbly regime. Dimensionless mass ratios of three model dispersants to the mineral oil necessary to establish emulsions were estimated from 2.6x10^-3 to 7.7x10^-3. Residence time distributions of seawater single- and mineral oil-seawater multi-phase flows, laden with dispersants, were also investigated. Increasing the dimensionless dispersant injection rate from 0 to 0.01 was observed to increase convective dispersion, which was confirmed by estimations of the vessel dispersion number and the Bodenstein number. The deposition and dissolution of asphaltenes in porous media, an important problem in science and macromolecular engineering, was for the first time investigated in a transparent packed-bed microreactor (μPBR) with online analytics to generate high-throughput information. Residence time distributions of the μPBR before and after loading with ~29 μm quartz particles were measured using inline UV-Vis spectroscopy. Stable packings of quartz particles with porosity of ~40% and permeability of ~500 mD were obtained. Temperature (25.0-90.0 °C), n-heptane composition (50.0-80.0 vol%), and n-alkane (n-C_5 to n-C_9) were all observed to influence asphaltenes deposition in the porous media, and reduced dispersion was obtained in the damaged packed-bed by estimating disperision coefficients and the Bodenstein number. Deposition by mechanical entrapment dominated the mechanism in all scenarios, as discovered by the simplified Kozeny-Carman and Civan's permeability-porosity relationships. Role of water on the deposition mechanism was then investigated. Porosity loss and permeability impairment of the porous media for water mass fractions of <0.001 to 34.5 wt% were investigated. Interestingly, a switch in the mechanism of water (from 0.030 to 3.18 wt%) on the accumulation was discovered. Analyses of porosity-permeability relationships revealed competition between adsorption and desorption followed by pore-throat plugging via mechanical entrapment for all mass fractions of water studied. For the dissolution of asphaltenes in porous media, many factors, such as shut-in time, temperature, Reynolds number, and n-heptane compositions, were studied, and the dissolution of asphaltenes was investigated. The work described within this dissertation undergirds that microchemical systems are promising tools that impact dispersant science and asphaltenes science. Microchemical systems also potentially aid the design of reservoir treatments.
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    Modeling of electromagnetic, heat transfer, and fluid flow phenomena in an EM stirred melt during solidification
    (University of Alabama Libraries, 2012) Poole, Gregory Michael; El-Kaddah, N.; University of Alabama Tuscaloosa
    A methodology is presented to simulate the electromagnetic, heat transfer, and fluid flow phenomena for two dimensional electromagnetic solidification processes. For computation of the electromagnetic field, the model utilizes the mutual inductance technique to limit the solution domain to the molten metal and magnetic shields, commonly present in solidification systems. The temperature and velocity fields were solved using the control volume method in the metal domain. The developed model employs a two domain formulation for the mushy zone. Mathematical formulations are presented for turbulent flow in the bulk liquid and the suspended particle region, along with rheological behavior. An expression has been developed--for the first time--to describe damping of the flow in the suspended particle region as a result of the interactions between the particles and the turbulent eddies. The flow in the fixed particle region is described using Darcy's law. Calculations were carried out for globular and dendritic solidification morphologies of an electromagnetically-stirred melt in a bottom-chill mold. The coherency solid fraction for the globular solidification morphology was taken to be 0.5, while the coherency for dendritic morphology was 0.25. The results showed the flow intensity in the suspended particle region was reduced by an order of magnitude. The effect of the heat extraction rate on solidification time was investigated using three different heat transfer coefficients. The results showed that the decrease in solidification time is nonlinear with respect to increasing heat transfer coefficient. The influence of the final grain size on the damping of the flow in the suspended particle region was examined, and it was found that larger grain sizes reduce the extent of flow damping.