Doctor of Philosophy, The Ohio State University, 2023, Earth Sciences

One of the most important features of our planet is its ability to sustain life in multi million year timescales. This ability largely depends on Earth's internal system in regulating the global carbon cycle. One of the key processes that regulates the global carbon cycle is weathering of silicate rocks. As such, a refined understanding of the silicate weathering system and its role in regulating the global carbon cycle in multi million year timescales is essential in predicting the fate of our planet amid the current and future increase in anthropogenic atmospheric CO2 concentrations. However, characterizing and identifying the direct or indirect evidence of changes in the global carbon cycle in the rock record is not trivial. First, the signals preserved in the rock record are prone to secondary alteration. Second, the traditional geochemical proxies can produce non-unique interpretations. My research is, therefore, aimed at addressing these issues by investigating and constraining the extent of diagenetic processes and elucidating possible links between tectonics and changes in silicate weathering during the Ordovician Period using novel geochemical techniques and numerical modeling. This research is broken down into three separate projects and presented in Chapter 2 through Chapter 4 of this dissertation. The study presented in Chapter 2 uses bulk carbonate measurements of calcium isotopes (δ44/40Ca) and trace element concentrations to constrain the extent of diagenetic processes affecting the δ13C record from the Middle Ordovician. The data and numerical models presented in this study suggest that variations in Sr/Ca and δ44/40Ca from Meiklejohn Peak correspond to changes in the dominant carbonate primary mineralogy and early marine diagenesis. However, the δ13C seem to reflect a primary change in the dissolved inorganic carbon (DIC). The positive shift recorded as the MDICE (Middle Darriwilian Carbon Isotope Excursion) likely represents a transient increas (open full item for complete abstract)

Committee: Matthew Saltzman (Advisor); John Olesik (Committee Member); Derek Sawyer (Committee Member); Elizabeth Griffith (Committee Member) Subjects: Earth; Geology

Doctor of Philosophy, The Ohio State University, 2023, Earth Sciences

Our understanding of the Earth's multimillion-year carbon cycle, with primary implications for the evolution of life, depends on our ability to decipher information encoded in chemical signals of shallow marine sediments. This dissertation attempts to develop our knowledge of two main topics: (1) the causes of multimillion-year global climate change in terms of changes in the sources and sinks of atmospheric carbon dioxide (CO2), and (2) the causes and meaning of post-depositional alteration of shallow marine sediments with respect to chemical proxy records of the evolution of global (and/or local) Earth processes. To this end, this work applies radiogenic strontium and neodymium (87Sr/86Sr, εNd(t)) and stable calcium (δ44/40Ca) isotopic records in bulk carbonate rocks and conodont apatite from Middle–Late Ordovician (Darriwilian–Katian stages; ~470–450 million years ago, abbrev. Ma) sections in the Antelope Range, central Nevada; Clear Spring, Maryland; and the Fjacka and Kargarde sections of the Siljan district, Dalarna province, central Sweden. Bulk rock samples from the tropical Middle–Late Ordovician setting of the Antelope Range, Nevada were analyzed for proxy records of regional and global continental weathering source lithology (87Sr/86Sr and εNd(t)) which were paired with published paleotemperature proxy measurements (δ18O) of conodont apatite from the same section. This paired suite of proxy records is used to test the hypothesis that low-latitude island arc accretion during the Middle–Late Ordovician Taconic Orogeny enhanced the weatherability of Earth's crust, increasing the rate of CO2 removal by the weathering of mafic silicate minerals and producing the global cooling observed in the Middle–Late Ordovician paleotemperature record. These records show coeval inflections in 87Sr/86Sr and εNd(t) values at ~463 Ma that reveal the influence of tectonic uplift and enhanced weathering of mafic ophiolite provinces on the Taconic margin. This change in weather (open full item for complete abstract)

Committee: Matthew Saltzman (Advisor); Audrey Sawyer (Committee Member); Elizabeth Griffith (Committee Member); William Ausich (Committee Member) Subjects: Chemistry; Earth; Geochemistry; Geology

Doctor of Philosophy, The Ohio State University, 2020, Earth Sciences

In the ocean and on land, many biogeochemical processes have feedbacks on climate. How these processes affect climate or respond to climate changes over long timescales is not always well understood as they are difficult to study in the modern day. The research reported here aims to better understand some of these processes, specifically erosion and sediment deposition, as well as the biogeochemical cycling of barium in the oceans. This research is separated into four projects that use geochemical and computational techniques to link long-term regional climate changes with atmosphere and ocean dynamics. The first two projects use samples from the Arabian Sea, collected during International Ocean Discovery Program Expedition 355 Arabian Sea Monsoon. During this expedition two sites were drilled, Sites U1456 and U1457 located within Laxmi Basin in the Arabian Sea. Samples range in age from 0-11 Ma. In project one, strontium isotope ratios (87Sr/86Sr) from pore fluids from Sites U1456 (n = 21) and U1457 (n = 20) were measured to characterize diagenetic reactions. Pore fluid 87Sr/86Sr is useful to establish fluid-rock reactions, sources, and fluid mixing that may have occurred after deposition, processes that could influence the signal recorded by proxy records from these marine sediment cores. The measured pore fluid 87Sr/86Sr has significant variations at both sites and three distinct zones of diagenetic processes are identified, with similar characteristics at both sites. In the second project, 87Sr/86Sr (n=127) and neodymium isotopes (εNd) (n=38) are measured from the separated clay fraction in sediments from the same cores to investigate their provenance. Provenance is the geographic origin of sediments deposited in a basin and is important to reconstruct so we can understand sediment pathways and constrain paleoclimate and erosion records. The records produced are also compared to 87Sr/86Sr and εNd of the carbonate-free bulk sediment from the same sites in ord (open full item for complete abstract)

Committee: Elizabeth Griffith (Advisor); Andrea Grottoli (Committee Member); Matthew Saltzman (Committee Member); Audrey Sawyer (Committee Member) Subjects: Geochemistry; Geology; Paleoclimate Science

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, The Ohio State University, 2017, Nuclear Engineering

Pyroprocessing is an electrochemical method that is capable of separating uranium (U) and minor actinides from LiCl-KCl eutectic salt where used nuclear fuel (UNF) is dissolved. During the process, fission products including rare earth metals (RE) continually accumulate in the salt and eventually affecting uranium recovery efficiency. To reduce the salt waste after uranium and minor actinides recovery, electrolysis is performed to drawdown rare earth materials from molten salt to restore salt initial state. Present research focus on the development of RE fundamental physical properties in LiCl-KCl eutectic salt. These properties includes apparent potential, activity coefficient, diffusion coefficient and exchange current density. Additional properties including charge transfer coefficient and reaction rate constant are calculated during the analysis. La, Nd and Gd are three RE that we are particularly interested in due to the high ratio of these elements in UNF (La, Nd), the well-studied properties in dilute solution to provide a base for comparison, and the highest standard potential among all RE (Gd). Fundamental properties of La, Nd, Gd in LiCl-KCl eutectic salt are studied at a temperature ranging from 723 K to 823 K and RE concentration ranging from 1 wt% to 9 wt%. These properties are studied by electroanalytical methods including Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), Tafel method, Chronocoulummetry (CC) and Chronopoentiometry (CP). BET model that considers the RE adsorption on the electrode is developed for diffusion coefficient analysis. Electrode kinetic model is developed to account for mass transfer effect during the analysis of exchange current density. Correlations of diffusion coefficient, apparent potential, exchange current density with temperature and concentration are developed. These fundamental data are integrated with a electrolysis model to predict the electrolysis process for RE drawdown from LiCl-KCl sa (open full item for complete abstract)

Committee: Jinsuo Zhang (Committee Chair); Marat Khafizov (Advisor); Lei Cao (Committee Member); Longya Xu (Committee Member) Subjects: Chemistry; Nuclear Engineering

Doctor of Philosophy, The Ohio State University, 1960, Graduate School

Committee: Not Provided (Other) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 1956, Graduate School

Committee: Not Provided (Other) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2014, Physics

THz systems are useful in a variety of fields such as astrophysics, analytical chemistry, security and communication. In this dissertation I present a computer simulation which allows evaluation of system performance, as well as the first submillimeter spectra of two molecular species: NdO and UO. The submillimeter spectra were recorded with a new high temperature spectroscopic system capable of temperatures of 2500 K while withstanding chemical and metallurgical attack. The simulation code addresses problems related to noise and nonlinear effects while maintaining a reasonable memory footprint and computational speed. It serves as a tool for system design and evaluation and bridges the information gap between technology developers and spectroscopists. The code is validated against experimental results from a well known ``standard'' spectrometer, as well as against fundamental theoretical results. It is then used to simulate a CMOS based system in development. The submillimeter spectra of NdO is presented and analyzed, building on the previous work in the optical region. The analysis results in improved spectroscopic constants, as well as constants for some never before measured states. In total, 1336 lines were recorded, of these, 643 were identified as belonging to series and 568 have vibronic assignments. The spectra also contain examples of resolved hyperfine structure for isotopes with nuclear spin, as well as examples of Ω doubling including one which resolved within the range of J recorded. Unlike NdO, UO has only one detectable isotope. As a result many fewer lines were recorded, a total of 274. However the analysis provided spectroscopic constants for four electronic states, including some vibrationally excited states which were previously unmeasured. In addition several series were identified that do not currently have assignments. In total 85 of the 274 lines were identified as belonging to series and 45 have vibronic assignments.

Committee: Frank De Lucia (Advisor); Douglass Schumacher (Committee Member); Thomas Lemberger (Committee Member); Ciriyam Jayaprakash (Committee Member) Subjects: Physics

MS, University of Cincinnati, 2002, Engineering : Electrical Engineering

Rare-earth sulfides provide a more stable alternative to reach Negative Electron Affinity (NEA) than the conventionally used cesiated surfaces which are sometimes deposited as alternate layers of Cesiumand Oxygen in the yoyo technique. In this thesis, we focus on a study of Neodymium Sulfide (NdS). The attractiveness of NdS resides in the predicted low work function value of 1.1 eV at room temperature, chemical and thermal stability, and high melting point of nearly 2200 C. The development of NEA surfaces with large quantum efficiency requires the mutual alignment of the crystalline energy levels at the semiconductor-surface junction. The choice of GaAs and related compounds as substrates is particularly attractive since the lattice constant of GaAs (5.6533A) closely matches that of NdS (5.6963A) in its cubic crystalline form. In this thesis, we report on the successful growth and characterization of NdS bulk samples and thin films. The bulk samples were grown by reacting the rare-earth element (Nd) with the rare-earth sesquisulfide (Nd2S3). The synthesized samples contain an oxysulfide impurity (Nd2O2S) which is removed using a carbon reduction method. NdS thin-films are formed by RF sputtering using a 2" target made out of the purified bulk samples. Thin films are deposited successfully on both Si and GaAs substrates. Both the bulk and thin film samples are characterized using X-Ray Diffraction and Raman Scattering techniques. The work function of the NdS bulk samples and thin films are also measured using a Kelvin probe technique.

Committee: Dr. Marc M. Cahay (Advisor) Subjects:

Master of Science, The Ohio State University, 2012, Geological Sciences

An understanding of past ocean circulation in the Arctic is critical for interpretations of past global ocean and atmospheric circulation, as well as predictions of future conditions. The Arctic Ocean plays a major role in global climate, due to its contributions to both the North Atlantic Deep Water (and subsequently the Atlantic Meridional Overturning Circulation) and the planet's albedo (due to sea ice cover). A sediment core from the Northwind Ridge in the western Arctic Ocean, ~800 km north of Alaska, has been sampled for measurement of radiogenic isotope ratios of neodymium and strontium. Sediment grain coatings were leached from the bulk sediment and measured for 87/86Sr and εNd, a proxy for seawater source. Two leaching solutions, one using buffered acetic acid and the second using hydroxylamine hydrochloride, were applied to sediments. Strontium data suggests that acetic acid best captures the seawater signal, while hydroxylamine hydrochloride leaching likely caused clay contamination of the hydrogenous data. εNd ratios were compared with independent lithologic proxies measured on the core and with results of earlier radiogenic-isotope studies in the Arctic Ocean. Data obtained suggest that radiogenic waters dominated the western Arctic Ocean during the estimated Early Pleistocene, probably due to increased Pacific water inputs and/or enhanced brine exclusion from sea ice formation on the Siberian shelves. These conditions likely indicate relatively warm climatic environments with predominantly seasonal sea ice, and thus can be potentially used as a paleo-analog for the projected near-future state of the Arctic. Further upcore, in the estimated Middle to Late Pleistocene, εNd values decrease overall, with high-amplitude fluctuations corresponding to glacial-interglacial cyclicity. Strongly non-radiogenic values in glacial intervals suggest the predominance of inputs from the Canadian Shield eroded by the Laurentide ice sheet. More radiogenic but gradually (open full item for complete abstract)

Committee: Lawrence Krissek PhD (Advisor); Leonid Polyak PhD (Committee Member); W. Berry Lyons PhD (Committee Member) Subjects: Geology; Marine Geology; Oceanography

PhD, University of Cincinnati, 2013, Engineering and Applied Science: Materials Science

Barium titanate is one of the most extensively studied dielectric and ferroelectric ceramic, continuing to be the material of choice for many applications. Its use as a dielectric for capacitors, thermisters, piezoelectric transducers and memory devices are well known. This research reveals that exceptionally high dielectric constants and other attributes desired for electronic and energy storage device applications are achievable by selected isovalent and aliovalent doping of barium titanate. Doping of barium titanate with Nd3+ and co-doping with Zr4+ is being studied to elucidate the complex interactions involved in the formation of grain boundary and surface barrier layers and other morphological characteristics. Observed dielectric relaxations of the system are related to charge compensation mechanisms and dielectric properties in terms of equivalent circuits, brick layer and Maxwell Wagner-Debye models. The perovskite structure of barium titanate admits either isovalent or aliovalent substitutions depending on dopant ionic radii. Isovalent substitutions generally modify the morphology of the ceramics and induce phase changes. Aliovalent substitutions, notably trivalent rare earth ions such as Nd, modulate electronic properties inducing semiconductivity at lower concentrations. At higher concentrations or under oxidizing conditions, ionic compensation retains insulation. The most remarkable feature observed in this study is the oxygen partial pressure driven solubility of Nd in barium titanate at intermediate dopant concentrations, generating surface barrier layer morphologies with gradient variations in Ti3+ from surface to the interior, exhibiting complex relaxation mechanisms. The study confirmed that macroscopic barrier layers over the sample surface and microscopic barrier layers in the grain boundaries profoundly influence dielectric properties, offering avenues for developing materials of high dielectric constant, low loss and good stability. Nd2O3 do (open full item for complete abstract)

Committee: Relva Buchanan Sc.D. (Committee Chair); Rodney Roseman Ph.D. (Committee Member); Jainagesh Sekhar Ph.D. (Committee Member); Vijay Vasudevan Ph.D. (Committee Member) Subjects: Materials Science