Doctor of Philosophy, The Ohio State University, 2011, Materials Science and Engineering

A persistent concern for applications of artificial graphite materials is loss of graphite due to thermal oxidation reactions with air or steam. Oxidation is insidious since it enlarges the inherent pores, which rapidly degrades microstructure and properties. Artificial graphites vary in their initial pore microstructure, yet the currently used 2D Random Pore Model (2D-RPM) cannot accurately predict oxidation rates from initial microstructure. Therefore, empirical methods have remained widely used to quantify oxidation rates. This goal of this dissertation work was to predict the oxidation rates of artificial graphite during isothermal air oxidation. A new analytical 3D Random Pore Model (3D-RPM) was created to account for uniform and nonuniform oxidation. In the model, the pore microstructure is created by randomly placed spheres of initial number per unit volume and initial radius. For uniform oxidation, it is assumed that all the spheres are growing at a constant rate. For nonuniform oxidation, there is a sample size and the internal oxidation front moves in one direction at a constant rate connecting the pores as it moves inward. The front rate is presumed to be a function of initial pore microstructure. The general formulation of the nonuniform 3D-RPM can account for surface and sample size effects on oxidation and includes uniform oxidation as a special case. The model inputs can be estimated from experimental data. This work was also the first application of a phase field model to visualize and quantify the evolution of pore microstructure in artificial graphite. The phase field model was validated with the 3D-RPM. Importantly, the phase field simulations provided the link between the model inputs and the pore clusters that form as a result of sphere overlap. Additionally, oxidation experiments were performed to investigate pore microstructure evolution and validate the models. It was found that the evolution in the number of pores in both the experiments an (open full item for complete abstract)

Committee: John Morral (Advisor); Jianjun Guan (Committee Member); Glenn S. Daehn (Committee Member); Charles H. Drummond, III, (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 2005, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1965, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1967, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy (PhD), Ohio University, 2024, Physics and Astronomy (Arts and Sciences)

The primary focus of this dissertation is the study of carbon and coal, particularly its atomistic dynamics in the conversion process to graphite or carbon foams and its interactions with plastics. Given the intricate molecular structure of coal, initial research was conducted on simpler amorphous-phase carbon structures, including amorphous graphite, multi-shell fullerenes, and multi-walled carbon nanotubes, to leverage their physical properties for understanding coal chemistry. This foundational research provided insights into fundamental properties such as interatomic interactions, thermal conductivity, and mechanical characteristics. The dissertation, organized largely as a collection of published works, explores the formation, structure, and properties of layered carbons and coal. It includes practical applications, such as coal carbonization, graphitization processes, and the development of carbon-plastic composites. The comprehensive exploration of these topics offers significant contributions to both the fundamental understanding and industrial application of coal and amorphous carbon materials.

Committee: David Drabold (Advisor) Subjects: Condensed Matter Physics; Physics

Doctor of Philosophy in Engineering, Cleveland State University, 2024, Washkewicz College of Engineering

Nonlinear hereditary inelastic deformation behavior can occur in many materials utilized at elevated service temperatures. This behavior can include creep, rate sensitivity, and plasticity. Accurate assessments of nonlinear stress and deformation behavior are important in predicting the operational life and overall performance of critical engineering systems. Inelastic constitutive models have been developed and deployed to meet these assessment needs. The models must predict nonlinear behavior under complex thermomechanical load paths. This includes capturing phenomena such as Bauschinger's effect, cyclic softening and hardening, stress relaxation, and ratcheting when present in high-temperature applications. This dissertation provides a literature review that details the development of inelastic constitutive modeling as it relates to polycrystalline materials. This review distinguishes between inelastic constitutive models that account for nonlinear behavior at the microstructural level, time independent classic plasticity models, and time-dependent unified models. Emphasis is placed on understanding the underlying theoretical framework for unified viscoplasticity models where creep and classical plasticity behavior are considered the result of applied boundary conditions instead of separable rates representing distinct physical mechanisms. This review also discusses recent topics in constitutive modeling that offer new techniques that bridge the gap between the microstructure and the continuum. Focus has been given to material science models that physically explain nonlinear behavior at the microstructural level. An understanding of material microstructure is always necessary in developing accurate multiaxial continuum-level constitutive models that characterize the responses of engineering components modeled with continuum-level perspective. Many forms of inelastic constitutive models are presented that include differential formulation (open full item for complete abstract)

Committee: Josiah Owusu-Danquah (Committee Chair); Stephen Duffy (Committee Member); Andrew Resnick (Committee Member); Jerzy Sawicki (Committee Member); Nigamanth Sridhar (Committee Member); Anne Campbell (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Civil Engineering; Materials Science; Mechanics; Nuclear Engineering

Doctor of Philosophy (PhD), Ohio University, 2022, Physics and Astronomy (Arts and Sciences)

Despite the long standing history of the research, production, and application of amorphous and glassy materials, generating good quality models still remains a challenge. The challenge arises from the inherent lack of the long range order, characteristic of crystals, in amorphous materials. Researchers have developed various techniques to create models of amorphous materials ranging from random Monte Carlo to classical molecular dynamics and from ab initio to the most recent machine-learned methods. In this dissertation, we apply force enhanced atomic refinement (FEAR) whereby experimental information from diffraction measurements are used jointly with ab initio density functional theory (DFT) based energy minimization to produce models of various amorphous materials that agree with diffraction data and are a suitable energy minimum of the chosen interatomic potential functions. By generating models of metal oxides and chalcogenides, we show that this method is broadly applicable to amorphous material if the experimental diffraction data is available. We used this to study the annealing induced changes in the structure of ZrO2-Ta2O5, a potential candidate for mirror coatings for the Laser Interferometer Gravitational-wave Observatory (LIGO) interferometer mirrors. We find that annealing increases the fraction of corner-shared metal-oxygen polyhedra in this material. Motivated by interest in carbonaceous materials, we studied the graphitization of carbon at temperatures near 3000 K. For the first time, we accurately simulate the process of graphitization and the mechanisms of layering. We have seen that individual layers of amorphous graphite are topologically disordered with some pentagon and heptagon carbon rings and have studied the effects of this disorder on charge density distribution, electronic density of states, and electronic conduction. The study of carbonaceous materials was extended to study the reactivity of carbon surfaces to diff (open full item for complete abstract)

Committee: David Drabold (Advisor); Eric Stinaff (Committee Member); Gang Chen (Committee Member); Jason Trembly (Committee Member) Subjects: Physics

Doctor of Philosophy (Ph.D.), University of Dayton, 2021, Materials Engineering

Macroscopic assembly of graphene into 2D films or paper is a new form of graphene which utilizes its exceptional properties. In this effort several fabrication processes of graphene-based paper were studied, and the mechanisms of thermal management and deicing were investigated. The details of these techniques were studied and their effect on the structure, quality, and in-plane thermal conductivity of graphene-based paper was evaluated. The techniques used to prepare graphene-based paper were chemical vapor deposition (CVD), hot pressing of graphene slurry, and evaporation induced self-assembly (EISA). The thermal and electrical conductivities of the resulting papers were measured, and various structural characterizations were made, including scanning electron microscopy (SEM), Raman spectroscopy, X- ray diffraction (XRD), small angle X-ray scattering (SAXS), and optical microscopy. SEM images showed the morphology of graphene-based paper made by the different techniques. XRD patterns had a sharp peak at 26.5° to show that the matching of crystallinity for graphene paper prepared via different techniques. SAXS patterns showed high directionality for CVD graphene-based paper. In-plane thermal conductivity measurement was performed using custom-built steady state in-plane thermal conductivity device. According to the measurements of in-plane thermal conductivity, CVD graphene-based paper has highest thermal conductivity than hot pressing and EISA techniques because of long phonon mean path, absence of defects and highly orientation of CVD graphene-based paper. This was important because heat spreaders made from high thermal conductivity materials are one of the most effective techniques used to dissipate heat generated in microelectronic devices, thereby enhancing the performance and reliability of electronics. A graphene-based paper composite panel was fabricated using a wet layup / vacuum bagging technique to study the mechanism of graphene-based paper for deic (open full item for complete abstract)

Committee: Khalid Lafdi (Advisor); Youssef Raffoul (Committee Member); Erick Vasquez (Committee Member); Donald Klosterman (Committee Member) Subjects: Materials Science

Doctor of Philosophy (Ph.D.), University of Dayton, 2021, Engineering

The planar and rigid nature of silicon-based electronics limit their reliability and integration into the next generation of electronics, like the Internet of Things (IoT) and wearable sensors. Unconventional electronics integrated with soft materials typically exhibit thermally limited performance due to low interfacial conductance and poor substrate thermal conductivity. To combat these issues, graphite nanoplatelets (GNPs) were used to increase the thermal conductivity of a flexible polydimethylsiloxane (PDMS) substrate by creating a percolating network of high thermal conductivity filler, increasing the substrate conductivity from 0.2 W-m-1K-1 to upwards of 1.8 W-m-1K-1, more than 9 times enhancement. This substrate material retained other useful properties including rheological behavior necessary for additive manufacturing, high temperature stability (upwards of 300C), flexibility (4 MPa compression modulus) and strong adhesion to device materials. This work is the first to demonstrate the direct transfer of the thinned AlGaN/GaN high electron mobility transistors (HEMTs) to the flexible polymeric nanocomposite substrate without an adhesive layer. The devices transferred to the PDMS composite substrates exhibited significantly lower self-heating temperatures experimentally (e.g., delta T = 24C at 30 mW) than those on PDMS when operated at comparable powers (15-50 mW), validating computational model results. These lower operating temperatures directly facilitate the operation of the devices at higher saturation currents and powers. The higher thermal conductivity of the PDMS composite substrate promotes heat conduction away from the device channel and effectively behaves as a flexible heat sink, which contributing to the high operating powers of 6 W-mm-1, especially compared to conventional flexible electronic substrates with low thermal conductivities (i.e. PDMS with no fillers). Additionally, the reduction of device temperatures at target operating powers resu (open full item for complete abstract)

Committee: Christopher Muratore PhD (Advisor) Subjects: Engineering; Materials Science

Master of Science (MS), Bowling Green State University, 2020, Physics

Semiconductor quantum dots are of remarkable interest as a versatile light-harvesting material in solar cells and a lot of other applications. Quantum dots are very tiny molecules and its efficient use in photovoltaics requires a considerable separation between holes and excited electrons so that they do not recombine to produce photons again. The research contained in this thesis investigates the use of Carbon-based quantum dots - Carbon NanoDots(CNDs) or Nanodiamonds - for charge separation to facilitate its use in photovoltaics. The electronic and optical properties of quantum dots are primarily dependent on their size due to quantum confinement. However, their properties can also be tuned by using other means. The introduction of organic ligands on the surface is one of those means. Our research primarily investigates the effect of functionalizing the CND surface with 4-ethynyl-N,N-bis(4-methoxyphenyl)aniline (MeOTPA) on its electronic and optical properties. All the calculations for electronic properties are done under the theoretical framework of Density Function Theory(DFT) using a package called Spanish Initiative for Electronic Simulations with Thousands of Atoms(SIETA). The optical properties are calculated using a Time-Dependant DFT package called Fast Absorption Simulation using TD-DFT(FAST). The results suggest that charge separation is possible in CNDs. The dependence of charge separation on the size of the quantum dot is also seen. The use of ligand also seems to sensitize CND to visible light.

Committee: Alexey Zayak Dr (Advisor); Haowen Xi Dr (Committee Member); Marco Nardone Dr (Committee Member) Subjects: Materials Science; Physics; Quantum Physics

Master of Science, The Ohio State University, 2019, Chemistry

Since its discovery in 1979, the solid electrolyte interface (SEI) has drawn attention due to its importance for efficient battery performance. Despite its significance, there is still some ambiguity with regards to how certain electrolytes form a protective interface to aid Li+ intercalation whilst others irreversibly degrade the anode structure. One of the most debated examples is the “EC-PC disparity” towards the graphite anode, where ethylene carbonate (EC) results in protective SEI formation whilst propylene carbonate (PC) leads to destructive graphite exfoliation. This study focuses on the correlation between the concentration of the Li+ salt, LiPF6 dissolved in PC and the growth of SEI on graphite. In-situ and in-operando electrochemical scanning tunneling microscope (STM) observation of the basal plane of highly oriented pyrolytic graphite (HOPG) is performed in 1 M, 2.5 M and 3 M LiPF6 dissolved in propylene carbonate (PC) in sequence to cyclic voltammetry (CV) and potential hold experiments. This technique allows the study of the topographic evolution of the basal plane and edge sites on HOPG with changes in the potential, as a result of solvent co-intercalation, reduction, graphite exfoliation and SEI formation. STM images obtained whilst holding the potential at selected values, gives an insight into the nature of SEI formation, in connection to the extent of regeneration of the graphite surface. It is found that below 0.9 V vs Li, solvent decomposition, followed by extensive graphite exfoliation takes place in the 1 M and to a lesser degree in 2.5 M LiPF6 electrolyte solutions. However, in the 3 M salt solution, graphite exfoliation is scarce and SEI formation is observed at potentials as high as 1.1 V vs Li, which clearly indicates a concentration dependent SEI formation on graphite. CV experiments conducted in parallel to EC-STM, provide further confirmation. The HOPG is cycled between 3 to 0.005 V vs Li in all three salt concentrations within Swa (open full item for complete abstract)

Committee: Anne Co Dr. (Advisor); Zachary Schultz Dr. (Committee Member) Subjects: Chemistry

Master of Science, University of Akron, 2019, Chemical Engineering

The next generation electronic devices are expected to be small in size and of magnified capacity. Denser packaging of the active components is important to miniaturize the electronic devices. Denser packaging is feasible only when heat generated by heat sources is quickly and effectively carried away to the heat sink. Next generation electronic devices with high performance microprocessors and integrated circuits along with diminished volume have led to major heat dissipation issue. Heat dissipation helps to control the temperature of the electronic devices at a desired level. Heat is dissipated to the heat sink from heat generator by the process of thermal conduction. Due to irregularities on the surfaces of the heat generator and heat sink, air is entrapped, and the air gap is formed in the path of thermal conduction. Air gap disturbs the thermal conduction as air is a really poor thermal conductor with a thermal conductivity of 0.026 W/mK at room temperature. Air acts as a thermal barrier preventing the effective heat transfer between the heat source and heat sink. Different kind of thermal interface materials are used to fill up the air gap between the heat generator and the heat sink to improve thermal conduction. Introduction of thermal interface material can significantly increase the performance of electronic device. In a typical power electronic package, a grease is used as thermal interface material. Thermal conductive paste with high thermal conductivity (much greater than air) fills up all the air gaps between the heat generator and the heat sink to improve the thermal conduction. Development of the thermal conductive paste with low thermal resistance, high thermal conductivity and low electric conductivity is challenging and the most important aspect in today's electronic industries. In the current study, we have tried to overcome this challenge by developing a thermally conductive grease with low thermal resistance, high thermal conductivity and low (open full item for complete abstract)

Committee: Jiahua Zhu PhD (Advisor); Rajeev Gupta PhD (Committee Member); Zhenmeng Peng PhD (Committee Member) Subjects: Chemical Engineering; Engineering; Polymers

Master of Science (MS), Ohio University, 2019, Mechanical Engineering (Engineering and Technology)

Aluminum alloys with improved electrical and mechanical performance are a highly sought-after due to their potential use as energy efficient conductors in power transmission, electronics, and aerospace systems. In this thesis, a novel hot extrusion alloying (HEA) process was used to synthesize aluminum/graphite nano-alloys using commercially available AA1100 and graphite nanoparticles (GNP) as precursors to improve electrical properties. The effects of GNP content from 0 – 1 wt.%, on the electrical and mechanical properties were evaluated. Results showed that the addition of 0.25 wt.% GNPs to the Al substrate improved its electrical conductivity by 2.1%, current density by 7.9%, ultimate tensile strength by 6.1% and yield strength by 30.3% compared to the control sample with no GNP additives. Improvements in electrical conductivity and current density were observed for all Al/GNP formulation at 60 °C and 90 °C. Ductility of the Al/GNP nano-alloys decreased with increasing GNP content. The improvement in Al/GNP electrical performance is attributed to GNP exfoliation at the temperatures and shear stresses experienced during hot extrusion, leading to the formation of highly conductive graphene particles.

Committee: Keerti Kappagantula (Advisor) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2019, Chemistry

Li-ion batteries are used in many devices, such as in cars, laptop computers, and cell phones. These batteries, however, have a short usable range and a limited life time. Currently, graphite is used as an anode material in most batteries, and even though graphite electrodes have good cycling performance, they have limited specific capacity of 372 mA
h/g. Operando spectra of a battery often consists of a strongly overlapping mixture of time dependent and independent resonances due to the compositional complexity. Here I report a new method called Derivative Operando (dOp) that improves the resolution of operando nuclear magnetic resonance (NMR) spectra by removing time independent signals and further distinguishes between time dependent signals associated with formation and removal of species. This approach not only provides better resolution but also more clearly reveals correlations between resonances and the chemical transformations occurring at a specific potential. With the dOp-NMR method we detect the formation of lithium graphite intercalation compounds (GICs), including the signatures of LiC72 and its precursors, which have been previously undetected. We also observe a clear correlation of the dOp 7Li NMR spectra of lithium metal dendrites on the counter electrode to the chemistry of the working electrode. Operando 7Li nuclear magnetic resonance (NMR), ex-situ 7Li magic-angle spinning (MAS) NMR and pair distribution function (PDF) methods are used to investigate the electrochemical lithiation and delithiation of 60 nm particles of tin. While the structural transformation pathways between Li-Sn intermetallics during lithiation and delithiation of Sn nanoparticles are somewhat consistent with the structural evolution of Li{Sn phases expected from the equilibrium binary phase diagram, there are some notable exceptions with the observation of a metastable phase Li2Sn3, and two vacancy rich metastable phases, Li7-zSn3, and Li13-dSn5 during delithiation. (open full item for complete abstract)

Committee: Anne Co (Advisor); Philip Grandinetti (Advisor); Yiying Wu (Committee Member); Robert Baker (Committee Member) Subjects: Analytical Chemistry; Chemistry; Materials Science; Physical Chemistry

Doctor of Philosophy, University of Akron, 2018, Mechanical Engineering

Flexible Li-ion batteries (LIBs) have strong forthcoming consumer market demand for use in different wearable electronic devices, flexible smart electronics, roll-up displays, electronic shelf labels, active radio-frequency identification tags, and implantable medical devices. This market demand necessitates research and development of these batteries in order to fulfill the energy and power requirements of these next-generation devices. In this study, the performance of semi-solid electrodes, which consists of active and conductive additive materials suspended in liquid electrolyte, for flexible LIBs is investigated through experiment and modeling. For the semi-solid graphite anode three different conductive additive materials of Super C45, Super P, and Ketjenblack are investigated. For the liquid electrolyte, which is mixed with graphite and conductive additive materials, lithium hexafluorophosphate salt (LiPF6) was dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). Several semi-solid graphite anodes with different compositions were fabricated and tested during the study. Over 65% of the specific discharge capacity to the theoretical capacity was achieved for the optimal composition of an anode. The semi-solid lithium cobalt oxide (LCO) cathode was also fabricated and tested simultaneously in the same lab. Subsequently, a full cell for a flexible LIB was fabricated based on the performances of the optimum LCO cathode and graphite anode half cells; then, the full cell was tested using galvanostatic measurements. A specific discharge capacity of over 60 mAh/g based on cathode mass was obtained when the cell was charged and discharged in the voltage range of 2.5-4.2V at a C-rate of C/40. In order to reduce the number of experiments and to achieve the desired energy capacity of the battery, a mathematical model was developed. This model is a multiphysics three-dimensional heterogeneous model. All necessary transport phenomena including th (open full item for complete abstract)

Committee: Siamak Farhad Dr. (Advisor); Alper Buldum Dr. (Committee Member); Yilmaz Sozer Dr. (Committee Member); Chen Ling Dr. (Committee Member); Kevin Kreider Dr. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 1987, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1972, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1952, Graduate School

Committee: Not Provided (Other) Subjects: Chemistry

Master of Science (MS), Wright State University, 2016, Physics

The effect of coatings on the heating curves of magnetic nanoparticles was studied in this Thesis. Iron cobalt vanadium (FeCoV) nanoparticles with oxide (CoOFe2O3) and graphite (C) coating to prevent oxidation, were synthesized through thermal plasma processing method. The magnetic nanoparticles had an average diameter of 30 nm. In the case of FeCoV with oxide coating, the initial diameter of the pure FeCoV nanoparticles on average was 30 nm but after oxidation 5 nm thick oxide layer was created. As a result of this oxidation, the magnetic core of FeCoV nanoparticles was shrunk from 30 nm to 20 nm in diameter. Graphite coating with a thickness of 10 nm was added uniformly to 30 nm in diameter of FeCoV nanoparticles. These magnetic nanoparticles were exposed to an ac applied magnetic field and their heating responses were measured. The measurements were done at frequency of 175 kHz and intensity of the magnetic field with different current values of 5 A, 10 A, and 15 A. The heating performance of magnetic nanoparticles described by Specific Absorption Rate (SAR) was calculated by finding the initial slope of the heating curve with respect to time. It was found that the maximum value of SAR was obtained when applied frequency and current were at 175 kHz and 15 A, respectively. Results were analyzed to find the coating effect on the heating rate. The most significant conclusion based on our research is to see that FeCoV magnetic nanoparticles with graphite coating had higher heating power than FeCoV with oxide coating.

Committee: Gregory Kozlowski Ph.D. (Advisor); Doug Petkie Ph.D. (Committee Member); Zafer Turgut Ph.D. (Committee Member) Subjects: Physics

Master of Science, University of Akron, 2016, Physics

Graphene and graphene based materials have great potential for their use in new technological applications. Here, we investigate the tribological properties of graphene, graphite, and graphene fluoride. We extensively studied these materials experimentally by using Atomic Force Microscopy (AFM) and theoretically by performing Molecular Dynamics Simulations (MDS). Experimental studies were based on rotational techniques to determine the directional dependence of the orthotropic sliding friction using Trace-Minus-Retrace (TMR) analysis of the height and lateral profiles. The MDS were focused on differences in sliding friction on the interior and at the edges of graphene with a fixed temperature for the 3A and 4A tip – surface separations. By performing both methods, experimental measurements, and atomistic simulations, the friction coefficients of graphene, graphene fluoride, and graphite were found to be in the range of 10-3 to 10-1. We found that atomic tip – surface interactions have an important effect on friction.

Committee: Alper Buldum Dr. (Advisor); Sergei Lyuksyutov Dr. (Advisor); Robert Mallik Dr. (Committee Member) Subjects: Materials Science; Molecular Physics; Nanoscience; Nanotechnology; Physical Chemistry; Physics