Browsing by Subject "Nickel"
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Item Controlling microstructure in nickel 200, titanium grade 2, and titanium grade 5 for the calibration of ultrasonic microstructure characterization(2018-05) Schick, Matthew Brian; Taleff, Eric M.Ultrasonic testing is a promising technique by which to nondestructively determine the subsurface material microstructure characteristics of metallic components. Development of this technique requires reference specimens of known microstructure by which to calibrate the ultrasonic signal response. Such reference specimens were produced in Nickel 200 (commercial-purity Ni or Ni 200), Titanium Grade 2 (commercial-purity Ti or TiGr2) and Titanium Grade 5 (Ti-6Al-4V or TiGr5) materials in the laboratory. The microstructures produced and methods of their production are presented and discussed. Particular attention is given to techniques appropriate in the general research laboratory environment. Recrystallized grain size is controlled across a wide range in the Ni 200, TiGr2, and TiGr5 materials by annealing after cold rolling. Heat treatments and hot compression further produced fully lamellar, duplex, and equiaxed (globular) microstructure forms in the TiGr5 material. The theory of ultrasonic signals interacting with grain boundaries and grain/phase interfaces will be discussed in light of the microstructures produced within these specimensItem Hierarchical three-dimensional Fe-Ni hydroxide nanosheet arrays on carbon fiber electrodes for oxygen evolution reaction(2014-05) O'Donovan-Zavada, Robert Anthony; Manthiram, ArumugamAs demands for alternative sources of energy increase over the coming decades, water electrolysis will play a larger role in meeting our needs. The oxygen evolution reaction (OER) component of water electrolysis suffers from slow kinetics. An efficient, inexpensive, alternative electrocatalyst is needed. We present here high-activity, low onset potential, stable catalyst materials for OER based on a hierarchical network architecture consisting of Fe and Ni coated on carbon fiber paper (CFP). Several compositions of Fe-Ni electrodes were grown on CFP using a hydrothermal method, which produced an interconnected nanosheet network morphology. The materials were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical performance of the catalyst was examined by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The best electrodes showed favorable activity (23 mA/cm², 60 mA/mg), onset potential (1.42 V vs. RHE), and cyclability.Item Mechanistic insights into heterogeneously catalyzed methane reactions(2017-05) Brush, Adrianna; Mullins, C. B.; Humphrey, Simon M; Heller, Adam; Hwang, Gyeong; Henkelman, GraemeCatalysts play an exceptionally important role in our society. Most synthetic materials rely on a catalyst at some point during their production, and the efficiency improvements due to catalysts are key to achieving the goal of sustainable human existence. Methane reactions have become important due to methane’s increasing source for energy and as a chemical feedstock. Understanding the mechanisms involved in catalyzed methane reactions will help direct future catalyst research. In this dissertation, we investigate mechanistic aspects of methane reactions over heterogeneous catalysts. Using model studies, we explore the surface structures and mechanism of O-H bond dissociation of methanol, a methane derivative, coadsorbed with hydrogen on Au(111). Using a classical catalyst reactor, methane reforming reactions and methane dissociation over molybdenum carbide based catalysts were investigated. We determined that Ni/Mo₂C will simultaneously catalyze the Dry Methane Reforming and Steam Methane Reforming reactions, with the resulting syn-gas ratio (H₂:CO) capable of being “tuned” from 0.9 to 3.0 by adjusting the ratio of H₂O:CO₂ in the reactant oxidant mixture. With an interest in developing transient techniques, we developed a novel apparatus capable of utilizing isotopically labeled gases more efficiently than current designs for Steady State Isotopic Transient Kinetic Analysis (SSITKA) experiments. This more efficient design allows more experiments to be performed. Using this apparatus, we investigated the methane dissociation mechanism over commercial Mo₂C. We found that carbon exchange did not occur between the methane and the Mo₂C carbide carbon, in contradiction to previous studies’ findings. Further, the dissociation of methane over Mo₂C was determined to involve a single C-H bond dissociation. This dissertation provides insights into the mechanisms behind heterogeneously catalyzed methane reactions, particularly methane reforming reactions over Mo₂C based catalysts. In addition, valuable isotopic experimental techniques, such as SSITKA, can benefit from the efficiency improvements offered by the Pulse Injection Apparatus, facilitating more robust investigations into catalytic mechanisms and kineticsItem Photoluminescence and stability of perovskite-phase CsPbI₃ nanocrystals and development of nickel metal-organic decomposition inks(2022-12-02) Abney, Michael Keith; Korgel, Brian Allan, 1969-; Ekerdt, John G; Milliron, Delia J; Vanden Bout, David ALead halide perovskite nanocrystals (LHP NCs) exhibit interesting and exceptional optical properties such as near-unity photoluminescence (PL) quantum yield and narrow PL emission line widths. As a result, LHP NCs have demonstrated promising potential in an array of optoelectronic devices such as photovoltaics (PVs), light-emitting diodes (LEDs), optical detectors, and lasers. For CsPbI₃ NCs in particular, one of the major obstacles to their commercial success is structural instability of the perovskite phase, which must be managed. Here, a closer look is taken at the PL emission of CsPbI₃ NC films and how it is affected by light and environmental conditions. The thermal phase stability of CsPbI₃ and the impact of surface area and composition are also investigated. Light-induced changes in photophysical and electronic properties in LHPs can affect their performance in device applications. It is revealed that light excitation induces a slow, reversible enhancement in PL lifetime and intensity in films of perovskite-phase CsPbI₃ NCs. Placing the films under vacuum or nitrogen for several minutes was also found to increase the PL lifetime and intensity. A model of slow, humidity and light-sensitive surface states in CsPbI₃ NCs is proposed. Perovskite-phase CsPbI₃ nanocrystals convert to the optically inactive δ-phase at elevated temperature. Alloying with Br was found to improve the phase stability when the films were relatively thin. Films of mixed-halide CsPbI₂.₅Br₀.₅ nanocrystals less than 30 nm thick showed no conversion to the δ-phase even after 1 hour of heating at 250°C, while thicker films still reverted to the δ-phase after heating. These results show that compositional changes and film thickness can have a significant, cumulative effect on the stability of perovskite nanocrystal films. The role of surface area/energy in CsPbI₃ nanocrystal stability is discussed. CsPbI₃ NC-based solar cells were successfully fabricated. This inspired collaborative work on the development of printable, conductive metal-organic decomposition (MOD) inks, which could play a role in the contacts of perovskite PV for low-cost, flexible, and low-temperature applications. Early development and characterization of a screen-printable, air-curable Ni-based MOD ink is detailed. Current performance of this ink is limited by residual carbon contamination, which is a focus of further development.Item Transition metal catalyzed regioselective carbon-carbon bond formation mediated by transfer hydrogenation(2015-05) Sam, Brannon; Krische, Michael J.; Anslyn, Eric V; Dong, Guangbin; Keatinge-Clay, Adrian T; Kerwin, Sean MOne of the more formidable challenges in the synthesis of complex organic molecules remains the efficient formation of carbon-carbon bonds. The development of a broad class of reactions to achieve this goal involves the addition of carbon based nucleophiles to carbonyl and imine compounds. Until recently, classical approaches to carbon-carbon bond formation generally required the use of stoichiometric pre-formed organometallic reagents to serve as nucleophiles, which translate into stoichiometric organometallic byproducts. In an effort to minimize nucleophile pre-activation and byproduct formation, our lab has developed efficient methods for carbonyl and imine additions via in situ formation of alkyl metal nucleophiles from π-unsaturates. The research reported herein describes our advances in an assortment of transition metal-catalyzed carbon-carbon bond forming reactions mediated by transfer hydrogenation, including regioselective hydrohydroxymethylation, hydrohydroxyfluoroalkylation, and hydroaminomethylation. Additionally, the investigation of regioselective carbonyl vinylation is reported.