Doctor of Philosophy, Case Western Reserve University, 2020, Chemical Engineering

Deep eutectic solvents (DES) are attracting attention for their potential use in energy storage applications such as redox flow battery. In such application, knowledge of the transport and electrochemical kinetics properties of DES is critically important. To date, attempts to measure the kinetics parameters of the Cu2++e <-> Cu1+ reaction in ethaline DES have yielded unreliable kinetic results. In this work, detailed recommendations are developed and verified for avoiding pitfalls in kinetics analysis of highly resistive DES electrolytes. Incorporating these recommendations, a comprehensive study of the kinetics and transport properties of the aforementioned redox reaction was carried out. Using steady–state and transient polarization measurements on RDE and microelectrodes combined with diffusion–reaction modeling, we demonstrate that the Cu2+/Cu1+ transition exhibits a charge transfer coefficient in the range of 0.49 – 0.54 and a reaction rate constant in the range (1.78 – 1.95) × 10-4 cm/s. The result indicates that the Cu2+/Cu1+ redox reaction in chloride–containing DES media suffers from sluggish charge transfer kinetics. The effects of DES composition and temperature on kinetics provided insights into the origins of the sluggish kinetics. Specifically, species complexation with Cl– which is present in excess in the chosen DES systems is shown to be the reason for slow charge transfer. For potential application in rare-earth metal recovery from spent waste, the electrodeposition of neodymium (Nd) metal from NdCl3–containing molten LiCl–KCl eutectic melts was investigated using voltammetry and diffusion–reaction modeling. Voltammetry studies confirmed that Nd electrodeposition is a two–step reduction process involving first a reversible one–electron transfer reduction of Nd3+ to Nd2+, followed by quasi–reversible reduction of Nd2+ to Nd metal. In the electrode potential range where Nd3+ is reduced to Nd2+, the peak current density measured in a voltammetry (open full item for complete abstract)

Committee: Rohan Akolkar Ph.D. (Committee Chair); Robert Savinell Ph.D. (Committee Member); Uziel Laudau Ph.D. (Committee Member); Mark De Guire Ph.D. (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, University of Akron, 2016, Chemical Engineering

Several studies have been published describing the corrosion inhibition effectiveness of surfactant admixtures by measuring the ability of surfactant molecules to physically adsorb onto metal surfaces. However, the effects of these admixtures have not been previously studied on coated metal surfaces to determine their corrosion inhibition mechanism. While corrosion protective coatings isolate exposed metal surfaces by forming a barrier between a substrate and the electrolyte, their performance is highly dependent on their interaction with their immediate environment. During the winter season in Snowbelt areas where chloride roadway deicers are greatly employed, coated metal surfaces in vehicles are constantly exposed to harsh and changing environments making them susceptible to failure. In order to extend the service life of these exposed coated surfaces, additional treatment by surfactant admixtures is regarded as an effective corrosion prevention strategy. In this work, the corrosion mechanism of surfactant admixtures on coated metal panels is evaluated by understanding the interaction of the liquid-solid interface. Despite the numerous mechanisms of inhibition behavior, it is hypothesized in this study that the contributions from inhibition solution systems create a protective layer over substrates by the formation of multi layers from aggregation or adsorption of surfactants. Furthermore, this study will help understand the relationship of the surface of corrosion protective coatings and the interaction with its environment. Electrochemical impedance spectroscopy (EIS) is applied to evaluate the corrosion performance of a high performance, low VOC, two component polyurethane enamel and a high performance UV-cured coating system on carbon steel alloy A36 under immersion testing of sodium chloride solutions of surfactant admixtures. This electrochemical technique permits the evaluation of the properties of the coating system by monitoring its degradation (open full item for complete abstract)

Committee: Chelsea Monty Dr. (Advisor); Scott Lillard Dr. (Committee Member); Gang Cheng Dr. (Committee Member); Christopher Miller Dr. (Committee Member); John Senko Dr. (Committee Member) Subjects: Automotive Materials; Chemical Engineering; Engineering; Materials Science; Physical Chemistry

Doctor of Philosophy, The Ohio State University, 2005, Materials Science and Engineering

High strength 7xxx aluminum alloys used widely in aircraft structure are very susceptible to intergranular corrosion (IGC). From a practical point of view, it is important to understand IGC in these alloys. Measuring the kinetics of IGC is not only a way to evaluate corrosion susceptibility, but also very useful for a predictive model for corrosion. Several AA7075 and AA7178 plates were used in this work. The foil penetration technique was used to measure the localized corrosion kinetics of the alloys in a NaCl solution and a new approach was developed to quantify the growth rates of sharp IGC fissures in a humid environment. Electrochemical properties of the alloys were studied by measuring the polarization curves. Electron microscopy and analytical techniques were used to observe the corrosion morphology and to understand the IGC mechanism. Localized corrosion kinetics were measured on several alloys with different grain aspect ratio to understand the influence of grain structure. Anisotropic corrosion kinetics were found on alloys with grain aspect ratio greater than 1. Metallographic cross-sections confirmed that the localized corrosion kinetics strongly depend on the IGC growth path, which was affected by the microstructural anisotropy of the material. It was also found that IGC morphology of AA7xxx was selective grain attack (SGA) in a NaCl solution and was sharp fissure in a humid environment. A statistical model for corrosion in AA7xxx was developed based on the grain structure of the material and the foil penetration data. Scenarios for SGA mechanism were proposed according to the statistical method and simulations. The sharp IGC fissure growth kinetics were found to be independent of the humidity from 96% to 58% RH due to little connection of the local sites to the external environment. The sharp IGC fissures were found to be filled with corrosion products that seem to drive fissure growth by an SCC mechanism.

Committee: Gerald Frankel (Advisor) Subjects: Engineering, Materials Science