Master of Sciences, Case Western Reserve University, 2014, Materials Science and Engineering

Owing to its thermodynamic control and conformal nature, gas-phase nitriding and carburizing of steels has for over a century been a popular method for increasing the hardness, wear-, and fatigue-resistance of ferrous components. Only in recent years (~3 decades) have such processes been successfully applied to stainless steels, under so-called paraequilibrium conditions whereby a truly colossal (>10^5 times the equilibrium concentration) supersaturation of interstitials can be achieved, thus imparting extraordinary improvements in the mechanical and electrochemical performance of the alloy. Such novel thermochemical techniques are relatively low-cost, industrially viable, and represent one of few value-added processes of a material that results in all gain and no loss. The thermodynamic origins of this metastable supersaturation, in particular carbon in austenitic 316, have been previously discussed within the context of the CALPHAD based multi-sublattice model for solid solutions. It is the present e ort of this work to review the complete thermodynamic database as applied to stainless steels, and develop a generalized approach for modeling metastable paraequilibria in both fcc austenitic and bcc ferritic (or martensitic) alloys upon low-temperature gas-phase nitriding or carburizing. A flexible and user-friendly program was developed to allow for predictions of the paraequilibrium carbon and nitrogen solubility in model binary to senary systems exposed to some carbon/nitrogen-rich ambient, as well as to model the solubility of carbon or nitrogen when a paraequilibrium, i.e. partitionless, carbide or nitride has formed. Changes in the paraequilibrium eutectoid temperature as a function of alloy content were also determined to predict the feasibility of an isothermal nitrogen- or carbon-induced ferrite (or martensite) to austenite (a (a') ¿ ¿) phase transformation. Such thermodynamic calculations can be used in optimizing interstitial hardening treatments of pre-e (open full item for complete abstract)

Committee: Gary Michal Prof. (Advisor); Arthur Heuer Prof. (Committee Chair); Frank Ernst Prof. (Committee Member); James McGuffin-Cawley Prof. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2006, Biophysics

The phase properties of lipids have very important consequences for membrane biology. Their influence ranges from the crystallization of membrane proteins, to drug delivery and domain formation in native membranes. To better understand the role that lipids play in these circumstances, it is necessary to study their physical properties. Therefore, the rules relating lipid phase behavior to their molecular structure need to be established. In this dissertation an effort is made to establish the relationship between the molecular structure of monoacylglycerols and their phase behavior. The major objective is to be able to rationally design lipids with required phase characteristics. The monoacylgylcerol/water phase systems were chosen for study. Using a database of homologous cis-monounsaturated monoacylglycerols with known phase characteristics, the temperature-composition phase diagrams of five monoacylglycerols were predicted. The phase diagrams of these monoacylglycerol/water systems were worked out. X-ray diffraction was used as a primary tool. In general, data was collected in a 0 to 65 %(w/w) water range, and from -15 C to 110 C. When creating a heating direction phase diagram, care was taken to set all samples into the solid Lc phase. Cooling direction phase diagrams were also worked out for these monoacylglycerols. Samples at room temperature were cooled down to -15 or -20 C. The predicted and experimental phase diagrams were compared to evaluate the efficacy of the predictions. The predictions were seen to agree with the experimantal data, within error. It was seen that better predictions were obtained when a larger number of homologous monoacylglycerols were considered when making the prrediction. The relationship between lipid molecular structure and phase behavior was thus established. Each monoacylglycerol studied was evaluated as a matrix from which membrane protein crystallization of at least one test membrane protein was attempted. Out of the five mono (open full item for complete abstract)

Committee: Martin Caffrey (Advisor) Subjects: Chemistry, Biochemistry

Doctor of Philosophy, University of Akron, 2007, Polymer Engineering

A free energy functional has been formulated based on an order parameter approach to describe the competition between liquid-liquid phase separation and solid-liquid phase separation. In the free energy description, the assumption of complete solvent rejection from the crystalline phase that is inherent in the Flory diluent theory was removed as solvent has been found to reside in the crystalline phase in the form of intercalates. Using this approach,we have calculated various phase diagrams in binary blends of crystalline and amorphous polymers that show upper or lower critical solution temperature. Also, the discrepancy in the χ values obtained from different experimental methods reported in the literature for the polymer blend of poly(vinylidenefluoride) and poly(methylmethacrylate) has been discussed in the context of the present model. Experimental phase diagram for the polymer blend of poly(caprolactone) and polystyrene has also been calculated. Of particular importance is that the crystalline phase concentration as a function of temperature has been calculated using free energy minimization methods instead of assuming it to be pure. In the limit of complete immiscibility of the solvent in the crystalline phase, the Flory diluent theory is recovered. The model is extended to binary crystalline blends and the formation of eutectic, peritectic and azeotrope phase diagrams has been explained on the basis of departure from ideal solid solution behavior. Experimental eutectic phase diagram from literature of a binary blend of crystalline polymer poly(caprolactone) and trioxane were recalculated using the aforementioned approach. Furthermore, simulations on the spatio temporal dynamics of crystallization in blends of crystalline and amorphous polymers were carried out using the Ginzburg-Landau approach. These simulations have provided insight into the distribution of the amorphous polymer in the blends during the crystallization process. The simulated results are in (open full item for complete abstract)

Committee: Thein Kyu (Advisor) Subjects:

PHD, Kent State University, 2024, College of Arts and Sciences / Department of Physics

This dissertation investigates the phase transitions from hadron to quark matter under non-equilibrium chemical conditions using the Chiral Mean Field (CMF) model, with a specific focus on the role of net strangeness and variations in charge and isospin fractions. By constructing detailed three-dimensional quantum chromodynamics (QCD) phase diagrams, this study elucidates how these factors influence chemical potentials, temperature, and the deconfinement process in environments similar to those found in protoneutron stars, binary neutron-star mergers, and heavy-ion collisions. The analysis reveals how these conditions impact the location of the critical endpoint, where the phase transition shifts from a first-order change to a crossover. Further exploration within this research addresses the significant impact of net strangeness on high-energy astrophysical phenomena, such as supernova explosions, neutron stars, and compact-star mergers. This work integrates recent theoretical developments in QCD critical points to provide a comprehensive overview of how non-equilibrium chemical conditions, particularly with respect to leptons, affect the deconfinement transition, narrowing the region of phase coexistence as observed in the interiors of cold catalyzed neutron stars. The findings emphasize the importance of including hyperons and strange quarks in theoretical models to better understand the complex nature of dense matter under extreme conditions. This dissertation contributes valuable insights into the dynamics of phase transitions in dense astrophysical objects, significantly advancing the field of high-energy astrophysics.

Committee: Veronica Dexheimer (Advisor); Antal Jakli (Committee Member); Hao Shen (Committee Member); Gokarna Sharma (Committee Member); Benjamin Fregoso (Committee Member) Subjects: Physics

Doctor of Philosophy, University of Toledo, 2021, Physics

This dissertation is a systematic computational investigation of transition metal nitrides in M4N structure and in two alloy systems of Ti1-xScxN and Ti1-xYxN (0 ≤ x ≤ 1). Transition metal nitrides constitute a class of materials which have been broadly applied in the industry of hard coatings and cuttings. Our objective is to expand the currently existing database of these materials by exploring their structural, mechanical, magnetic, electronic, and thermodynamic properties, stability and hardness using the state-of-the-art first principles computational approach. Chapters 4 and 6 contain the main results and are summarized as follows. 1. We performed first-principles calculations with density functional theory on 28 metal rich cubic binary M4N structures. We provided a high through-put database of mechanical, electronic, magnetic, and structural properties for these compounds. We observed three compounds with Vickers hardness around or above 20 GPa, such as Re4N, Tc4N, and Mn4N (Chapter 4). We also identified 25 M4N compounds as mechanically stable while the remaining 3 (V4N, Nb4N, and Pt4N) as unstable. 2. We showed the relationship between the hardness and stability of these compounds and the density of states. We also calculated the magnetic properties of five magnetic compounds and exhibited that the consideration of electronic spin-polarization is very important in accurately calculating ground state energy and hence mechanical properties of these transition metal nitrides. 3. We also studied the phase stability, mechanical and electronic properties of two ceramic quasi-binary systems, Ti1-xScxN and Ti1-xYxN using density functional theory, cluster expansions and Monte Carlo simulations. We predicted strong exothermic mixing of TiN and ScN due to cationic similarity with the formation of 4 novel intermetallic compounds TiScN2, TiSc8N9, TiSc9N10, and Ti3Sc2N5 in the Ti1-xScxN system having hardness as high as 27.3 GPa. The phase diagram of Ti1-xScxN sys (open full item for complete abstract)

Committee: Sanjay Khare Dr. (Committee Chair); Jacques Amar Dr. (Committee Member); Richard Irving Dr. (Committee Member); Aniruddha Ray Dr. (Committee Member); Anju Gupta Dr. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2019, Materials Science and Engineering

Ni-based and Fe-based alloys are widely used structural materials for critical applications such as jet engines and load-bearing components. Materials design and optimization has been accelerated through the Integrated Computational Materials Engineering (ICME) approach. ICME relies on high fidelity thermodynamic and kinetic databases to simulate the composition-processing-properties relationships in materials. A novel extension to the diffusion multiple approach was developed exploring vapor-based surface treatments including aluminization of Ni-based systems and low-pressure carburization of Fe-based systems to generate composition profiles in multiple dimensions. The vapor-reacted treatments allow for high-throughput data generation across wide temperature-composition regimes that aren't achievable using traditional diffusion couple experiments. The Ni-Cr-Pt-Al and Fe-Cr-Mo-Ni-V-C alloy systems were studied for improved understanding of Pt-modified aluminides in thermal barrier coatings on airfoils and carbide formation in steels, respectively. A diffusion multiple of Ni, Cr, and Pt was annealed at 1200 °C for 100 hours for the establishment of the first reliable isothermal section phase diagram of the Ni-Cr-Pt ternary system using electron probe microanalysis (EPMA). Interdiffusion coefficients were also extracted from the measured diffusion concentration profiles using a forward simulation analysis (FSA) for the Ni-Cr, Ni-Pt and Cr-Pt binary systems. The impurity diffusion coefficient data obtained were combined with literature data to assess reliable Arrhenius equations for Pt in Ni, Ni in Pt, Cr in Ni, and Cr in Pt. Other pieces from the annealed Ni-Cr-Pt diffusion multiple were subjected to vapor phase aluminization at 1010 °C for 9 hours and pack aluminization at 1150 °C for 3 hours. Al pickup drastically increased from Cr to Ni to Pt. The Pt and Cr rich part of an isothermal section of the Pt-Cr-Al ternary system at 1010 °C and the Ni and Pt (open full item for complete abstract)

Committee: Ji-Cheng Zhao (Advisor); Alan Luo (Committee Member); Maryam Ghazisaeidi (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Toledo, 2017, Physics

This dissertation is a computational exploration of transition metal nitrides, a group of materials that have myriad applications in the hard coatings industry. We aim to explore their structural, mechanical, electronic and thermodynamic properties and their solid solutions, discovering trends and correlations of their bonding nature and cause of superior stability and hardness. Here are the major work and results: 1. We performed first-principles calculations with density functional theory on six cubic structural prototypes, zincblende, rocksalt, cesium-chloride, NbO, fluorite and pyrite. We observed a few compounds with Vickers hardness higher than 20 GPa, such as rocksalt-structure ScN, TiN, cesium-chloride-structure VN, NbO-structure CrN, MoN, WN, and pyrite-structure MnN2, PtN2. (Chapter 4, Chapter 5 and Chapter 6) 2. We established an anti-correlation between metallic compounds' total electronic density of states at the Fermi energy level, an indicator of metallicity and their shear-related mechanical properties, such as elastic constant C44, shear modulus, Pugh's ratio and Vickers hardness. (Chapter 4, Chapter 5 and Chapter 6) 3. Beyond single-cation phases, we further studied the phase equilibria of three ceramic quasibinary systems, Ti1-xZrxN, Ti1-xHfxN and Zr1-xHfxN. We analyzed the asymmetry of composition-dependent formation energy curves through two energetically partially canceling processes. We concluded that the absence of experimental observations of phase separation, as predicted by our calculations in Ti1-xZrxN and Ti1-xHfxN is probably due to a combined effect of insufficient undercooling, inadequate atomic diffusivity, and the initial energy barrier for chemical exchange with constrained lattices. (Chapter 8) 4. We also showed that mixing nitrides of same group transition metals does not lead to hardness increase from an electronic origin, but through solution hardening mechanism, a plastic phenomenon difficult to catch with first-pr (open full item for complete abstract)

Committee: Sanjay Khare (Committee Chair); Jacques Amar (Committee Member); Nikolas Podraza (Committee Member); Bo Gao (Committee Member); Daniel Georgiev (Committee Member) Subjects: Physics

Master of Science, The Ohio State University, 2011, Materials Science and Engineering

The Ni-rich corner of the 1200 °C isothermal sections of both the Ni-Al-Cr and Ni-Al-Mo ternary phase diagrams were obtained using diffusion multiples together with SEM imaging and electro-probe microanalysis (EPMA). In the Ni-Al-Cr system, composition regions of both the Cr-based bcc phase and the β-NiAl phase were observed to be very different from those reported in the literature. For instance, the bcc phase was found to have ~ 26 at% Ni solubility, more than double what has been previously reported in the literature and more consistent with the binary Ni-Cr phase diagram. In the Ni-Al-Mo system a new phase was discovered. This phase, Ni5Al2Mo8, exists in what appears to be a near stoichiometric composition. Its structure is yet to be determined. Reliable phase equilibrium information useful for superalloy development, especially the phase boundary between the fcc (γ) phase and the L12 (γ') phase was obtained for both ternary systems.

Committee: Ji-Cheng Zhao PhD (Advisor); Yunzhi Wang PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2009, Chemistry

To date, fifteen phases of ice have been discovered. Many of these phases occur in pairs consisting of a fully ordered member and a hydrogen bond (H-bond) disordered phase. The disordered phase contains the water oxygens in nearly the same positions as the fully ordered phase, but the orientations of hydrogens are disordered. Our research examines the phase transitions between members of these ordered/disordered pairs. These transitions are sluggish because they occur at such low temperatures that water molecules cannot easily rotate to rearrange the directions in which the hydrogen bonds point. It is defects in the ice lattice that make the transitions possible. For instance, ice Ih transforms to ice XI only when doped with hydroxide ions, but many questions linger about the mechanism since experiments suggest that hydroxide ions are not mobile near the transition temperature. In this dissertation, theoretical methods are introduced which are capable of describing the small energy differences among the innumerable H-bond configurations of the water molecules in ice. The theory uses input from periodic electronic density functional theory calculations for small unit cells to parameterize interactions in terms of the H-bond topology. This parameterization enables statistical mechanical calculations for systems large enough to approximate the thermodynamic limit. Our calculations were the first to confirm that ordinary ice, a disordered phase, transforms into a fully ordered counterpart, ice XI. For those disordered phases for which an ordered version has been experimentally characterized, our methods yield transition temperatures in good agreement with experiment. We also proposed a candidate structure to experimentalists for proton-ordered ice VI, for which an ordered version has yet to be observed. We have also extended these methods to describe the interactions of the H-bond topology with defects (ionic and orientational) and oxygen site-disorder. We have successf (open full item for complete abstract)

Committee: Sherwin J. Singer PhD (Advisor); James V. Coe PhD (Committee Member); Russell M. Pitzer PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy, Case Western Reserve University, 1990, Chemical Engineering

An entirely new type of electrochemical phase diagram, the electron number diagram, has been discovered. The theoretical foundation for the electron number diagram and its relationship to conventional potential-pH diagrams have been developed. Electron number diagrams are obtained by a thermodynamic transformation in which potential is replaced by a measure of the number of electrons. The chemical potential of electrons and the number of electrons are conjugate thermodynamic variables. The areas in which electron number diagrams provide information complementary to and in addition to that from conventional potential-pH diagrams have been identified. Experimental electron number diagrams have been constructed for the aqueous sulfur system. Two-dimensional sections of the three-dimensional electron number diagram at both constant pH and constant electron number have been determined and compared with the sections computed from theory. Agreement between the computed and measured diagrams has been found. A rigorous thermodynamic theory for complex aqueous redox systems has been developed and used for interpretation of the various types of electrochemical phase diagrams. The dimensionality of potential-pH and electron number diagrams has been related to the Gibbs phase rule analysis of aqueous redox systems. An efficient computational method, based on the theoretical analysis of complex aqueous redox systems, has been developed. The equations describing the equilibrium composition are obtained from a minimum set of formation reactions. The formation reactions use a set of reactants (components) whose chemical potentials are chosen to be the independent variables in the computation. This procedure permits the sequential rather than simultaneous solution of the equation set in the case of ideal solutions. Efficient stability criteria, obtained from theory, here used to determine the stability of solid phases. The algorithm was implemented on IBM PCs and compatible computers (open full item for complete abstract)

Committee: John Angus (Advisor) Subjects: Engineering, Chemical