Ceramic Materials Commons^™

Zirconium Carbide Based Materials For Extreme Aerospace Environments, Nathaniel Hyman Blatt

Doctoral Dissertations

This research focuses on the processing and properties of zirconium carbide-based materials to promote their use in extreme environment aerospace applications, including nuclear thermal propulsion and hyper sonics. Several carbide systems including ZrC, ZrC-Mo cermets, (Zr, Nb)C, and a high entropy carbide were developed. The ZrC-Mo cermet was studied extensively to understand the effect of starting carbide grain size on the final microstructure, composition, elastic moduli, hardness, fracture toughness, room and elevated temperature flexural strength, thermal diffusivity, electrical resistivity, thermal expansion coefficient, and thermal conductivity. It was shown that heat transport in the cermets was dominated by the ZrC phase …

Strontium Titanate For Capacitor And Energy Storage Applications At Cryogenic Temperatures, Hung Trinh

Doctoral Dissertations

This study investigates the dielectric properties of single crystal and ceramic strontium titanate (SrTiO₃) for cryogenic capacitor applications from room temperature to 4 K. Permittivity (k) and loss tangent are dependent on temperature, frequency, mechanical stress, and applied DC electric field. Accordingly, the dielectric constant and loss tangent were measured at various frequencies and DC bias levels. Loss tangent data are also presented as equivalent series resistance (ESR). For single crystal SrTiO₃, an impurity level of ≈500 ppm barium resulted in an increase of the maximum permittivity to approximately 50,000 at 6 K. This relatively high …

The Structure, Properties And Dissolution Behaviors Of Phosphate Glasses, Han Zhang

Doctoral Dissertations

The poor chemical durability remains a critical challenge for the application of phosphate glasses. This study investigates the compositional influences on the structure, properties and chemical durability of Li2O-ZnO-P₂O₅ glasses. Their structural characteristics were analyzed utilizing high-performance liquid chromatography, Raman spectroscopy, and X-ray photoelectron spectroscopy. The incorporation of (Li2O+ZnO) in LZeq glasses depolymerizes the phosphate network. In LZ40P and LZ45P glasses, Li⁺ initially replaces Zn²⁺ associated with non-bridging oxygens (NBOs) in Q² tetrahedra. Once the substitution in Q² is complete, further Li⁺ incorporation leads to the replacement of Zn²⁺ in Q^{1 …}

Investigating The Effects Of Fly Ash On The Properties Of Silica-Deficient High Alumina Materials, Sai Akshay Ponduru

Doctoral Dissertations

This research is made up of five studies mainly focused on attaining sustainability in high alumina cements like calcium aluminate cement (CAC) and calcium sulfoaluminate belite cements (CSAB) by partially replacing them with additives and supplementary cementitious materials (SCMs) like fly ash (FA). The first study focused on understanding the reaction kinetics of CAC and FA binders at different replacement levels (i.e. between 10%-to-50% by mass) and their effect on mechanical properties. It was also shown that the reactive nature of FAs can be determined by calculating a single parameter called number of constraints (nc) derived from topological constraint theory. …

Intragranular Tungsten-Titanium Carbide Composite Ceramics Via Gas-Solid Displacement Reactions, Ryan Daniel Dempsey

Doctoral Dissertations

"Research presented herein details the synthesis and characterization of nanocomposite ceramics featuring novel heterogeneous microstructures of potential interest in a variety of electrical and structural applications. Specifically, W-TiCy composite ceramics featuring tungsten nanoprecipitates located primarily within TiCy grains have been produced via sintering of intragranular nanocomposite powders produced via reaction processing-based techniques. This dissertation details the thermodynamic basis and applied kinetics of a processing scheme for fabricating nanocomposite ceramics whose morphological heterogeneity reflects that originally developed in the powder state. The first study in this series overviews the motivation for applying metallothermic displacement reactions, conducted through gaseous intermediates, to solid …

Mechanical Properties Of Boride Based Ceramics, Alec Murchie

Doctoral Dissertations

“This research focuses on the elevated mechanical properties of diboride based materials at room and elevated temperatures. These materials include a ZrB₂ ceramic, a ZrB₂-WC-SiC ceramic, and a (Hf,Mo,Nb,Ta,W,Zr)B₂ high entropy boride (HEB). The room temperature flexural strength for the ZrB₂ ceramic was 447 MPa and the fracture toughness was 2.3 MPa·m^1/2. The strength decreased to 196 MPa at 1800°C, and then increased to 360 MPa at 2300°C. The fracture toughness increased to 3.1 MPa·m^1/2 at 2200°C. The strength up to 1800°C was likely controlled by a combination of effects: surface damage …

Joining Of Ultra-High Temperature Ceramics To The Same And Refractory Metals Via Fusion Welding, Jecee Jarman

Doctoral Dissertations

"This research focuses on the joining of ultra-high temperature ceramics to either themselves or refractory metals/alloys via fusion welding and the mechanical strength of produced joints. The ceramics studied consisted of compositions within a diboride-carbide-carbide ternary system while metals studied consisted of molybdenum and a molybdenum alloy. SiC-ZrB2-ZrC ceramics on a binary join between pure SiC and the ternary eutectic composition were found to be weldable when SiC content was below ~57.5 vol%. Compositions above 57.5 vol% SiC were unweldable based on pitting and off-gassing behavior. Welded strength of ceramics was ~180-300 MPa in the SiC-ZrB2-ZrC ternary eutectic composition, ~180-220 …

Contributions To The Performance Of Thin Film Capacitors For High Reliability Applications, Daniel Krueger

Doctoral Dissertations

"Capacitors are critical devices in microelectronic assemblies that must be incorporated into electronic systems through a variety of ways such as integrated or discrete devices. This work has developed new thin film capacitors deposited directly onto multichip module or printed circuit board surfaces to benefit from closer integration that enhances system performance for use in high reliability applications. The capacitors serve as filters or provide tuning and energy storage functions. Unexpected performance was observed during development that included low adhesion of the films to the substrates, higher effective dielectric constants than reported in literature, and low yields. Three publications resulted …

Thermal And Mechanical Properties Of Novel Carbide Materials, Evan Charles Schwind

Doctoral Dissertations

"This research focuses on studying the thermal and mechanical properties of novel carbide materials at room and elevated temperatures. The novel carbide materials investigated include zeta phase tantalum carbide (ζ-Ta₄C_3-x) and a high entropy (Ta,Hf,Nb,Zr)C carbide. The electrical resistivity and thermal conductivity of zeta phase tantalum carbide (~96 wt.%) were measured as 160 ± 4.2 μΩ-cm and 9.6 W/m•K. These are higher and lower (respectively) than for cubic tantalum carbide, most likely due to planes of carbon vacancies present in the ζ-Ta₄C_3-x crystal structure. The thermal conductivity of (Ta,Hf,Nb,Zr)C was lower than any …

Studying The Effects Of Various Process Parameters On Early Age Hydration Of Single- And Multi-Phase Cementitious Systems, Rachel Cook

Doctoral Dissertations

”The hydration of multi-phase ordinary Portland cement (OPC) and its pure phase derivatives, such as tricalcium silicate (C₃S) and belite (ß-C₂S), are studied in the context varying process parameters -- for instance, variable water content, water activity, superplasticizer structure and dose, and mineral additive type and particle size. These parameters are studied by means of physical experiments and numerical/computational techniques, such as: thermodynamic estimations; numerical kinetic-based modelling; and artificial intelligence techniques like machine learning (ML) models. In the past decade, numerical kinetic modeling has greatly improved in terms of fitting experimental, isothermal calorimetry to kinetic-based modelling …

Fusion Welding Of Diboride-Carbide Ceramic Composites, Derek Scott King

Doctoral Dissertations

"Plasma and pulsed plasma arc welding (PAW and PPAW) processes were used to fusion weld ZrB₂ containing 20 vol% ZrC. Varying welding parameters resulted in changes in weld pool shape and size, and the size of ZrB₂ grains within the fusion zone. For PAW processes that resulted in a keyhole fusion zone (full penetration), the arc to workpiece power transfer efficiency was estimated to be 2 grain lengths were observed to decrease between binary PAW FZs (~1 mm in length), and binary PPAW FZs (~0.8 mm in length), and an increasing aspect ratio for ZrB₂ grains in …

Effect Of Solid Solutions And Second Phases On The Thermal Conductivity Of Zirconium Diboride Ceramics, Gregory John Kenneth Harrington

Doctoral Dissertations

"The research presented in this dissertation is focused on the thermal conductivity (k) of ZrB₂ ceramics. The goal was to develop a better understanding of how various solid solutions and second phases affect the thermal and electrical transport in ZrB₂, with a focus on the effect of C, W, and ZrC. The first study showed C additions improved densification and it was proposed that the reduction of boria was the impetus for this result. Boron carbide was formed by the reaction of excess C with reduced B and its formation was mitigated by the addition of ZrH …

Elevated Temperature Mechanical Properties Of Zirconium Diboride Based Ceramics, Eric W. Neuman

Doctoral Dissertations

"Research presented in this dissertation focused on the mechanical behavior of ZrB₂ based ceramic at elevated temperatures. Flexure strength, fracture toughness, and elastic modulus were measured at temperatures up to 2300ºC for three compositions: monolithic ZrB₂ (Z); ZrB₂ - 30 vol% SiC - 2 vol% B₄ C (ZS); and ZrB₂ - 10 vol% ZrC (ZC). In argon, Z, ZS, and ZC had strengths of 210 (at 2300ºC), 260 (at 2200ºC), and 295 MPa (at 2300ºC), the highest temperatures tested for each composition. Fractography was used extensively to characterize the strength limiting flaws as a function of temperature. Strength of ZS …

Bioactive Glass Scaffolds For The Regeneration Of Load-Bearing Bone, Xin Liu

Doctoral Dissertations

"Biocompatible scaffolds that replicate the structure and function of bone would be ideal bone substitutes for structural bone loss, provided they have the requisite mechanical properties for reliable long-term loading. In this dissertation, strong porous scaffolds of silicate 13-93 bioactive glass, created with two different microstructures, were evaluated to determine their mechanical properties and their capacity to regenerate bone in a rat calvarial defect model. Scaffolds with an oriented microstructure of columnar pores were prepared by unidirectional freezing of camphene-based suspensions, followed by thermal annealing and sintering. By optimizing the freezing conditions, annealing time, and sintering temperature, constructs (porosity = …

Thermal Properties Of Spinel Based Solid Solutions, Kelley R. Wilkerson

Doctoral Dissertations

"Solid solution formation in spinel based systems proved to be a viable approach to decreasing thermal conductivity. Samples with systematically varied additions of MgGa₂O₄ to MgAl₂O₄ were prepared and thermal diffusivity was measured using the laser ash technique. Additionally, heat capacity was measured using differential scanning calorimetry and modeled for the MgAl₂O₄-MgGa₂O₄ system. At 200⁰C thermal conductivity decreased 24% with a 5 mol% addition of MgGa₂O₄ to the system. The solid solution continued to decrease the thermal conductivity by 13% up to 1000⁰C with 5 mol% addition. The decrease in thermal conductivity ultimately resulted in a decrease in heat flux …

Processing And Characterization Of Boron Carbide-Hafnium Diboride Ceramics, Harlan J. Brown-Shaklee

Doctoral Dissertations

"Hafnium diboride based ceramics are promising candidate materials for advanced aerospace and nuclear reactor components. The effectiveness of boron carbide and carbon as HfB₂ sintering additives was systematically evaluated. In the first stage of the research, boron carbide and carbon additives were found to improve the densification behavior of milled HfB₂ powder in part by removing oxides at the HfB₂ surface during processing. Boron carbide additives reduced the hot pressing temperature of HfB₂ by 150⁰C compared to carbon, which reduced the hot pressing temperature by ~50⁰C. Reduction of oxide impurities alone could not explain the difference in sintering enhancement, however, …

Phase Equilibria In Iron Phosphate System, Liying Zhang

Doctoral Dissertations

"The main objectives of this research were to synthesize iron phosphate compounds, study phase equilibria in the iron phosphate system, focusing on the glass forming area, and investigate glass formability and properties based on the liquidus regions. Twelve iron phosphate compounds were successfully prepared and studied in terms of liquidus temperature or decomposition behavior. The liquidus surface of the Fe₃PO₇- Fe(PO₃)₃ system was re-determined and found to be significantly different from that originally presented by Wentrup in 1935. Eutectic points exist at 58.0 mole% Fe₂O₃ (1070⁰C), 42.7 mole% Fe₂O₃ (925°C), and 37.0 mole% Fe₂O₃ (907°C). The latter two eutectic points …

Ceramic Dielectrics For High Energy Density Capacity Application, Sheng Chao

Doctoral Dissertations

"The objective of this dissertation is to investigate the relationship between the processing parameters, microstructural development, defect chemistry and electrical properties of titanium oxide (TiO₂) dielectrics for high energy density capacitor applications. The effects of aliovalent dopants on the dielectric properties of TiO₂ ceramics were investigated, aiming to further improve the desired dielectric properties especially at elevated temperatures (up to 200°C). Due to the segregation of acceptor type impurities in the starting powders, space charge polarization took place in TiO₂ ceramics with relative large grain size (>̲500nm), leading to high dielectric loss and low energy storage efficiency. Increased ratio …

Anti Wetting Additives For Aluminosilicate Refractories In Molten Aluminum Contact Applications, Devdutt Pramod Shukla

Doctoral Dissertations

"Aluminosilicate based refractories are widely used in furnace installations for melting aluminum because they are inexpensive, readily available and generally exhibit the properties desired from a refractory material. However, they face severe corrosion and degradation issues due to the extremely reducing nature of molten aluminum alloys. Isothermal static cup testing is widely used as a tool to evaluate the performance of refractories against penetration by molten aluminum alloys. Various testing methods were reviewed and an upgraded static cup test was recommended. Commercially available aluminosilicate refractories were tested using this method and their results were studied in order to understand the …

Freeze Casting Of Bioactive Glass And Ceramic Scaffolds For Bone Tissue Engineering, Qiang Fu

Doctoral Dissertations

"The main objectives of this dissertation were to explore the production of bioactive ceramic and glass scaffolds with oriented pore architectures by unidirectional freezing of suspensions, and to characterize the mechanical and biological performance of the scaffolds. Freezing of aqueous suspensions of hydroxyapatite (HA) or bioactive 13-93 glass particles resulted in the formation of scaffolds with a lamellar-type microstructure (pore width = 5-30 µm). The addition of polar organic solvents (such as 60 wt% dioxane) to the aqueous suspensions markedly changed the morphology and size of the oriented pores, giving scaffolds with a columnar-type microstructure and larger pre width (90-110 …

Densification, Microstructure, And Mechanical Properties Of Zirconium Diboride Based Ultra-High Temperature Ceramics, Sumin Zhu

Doctoral Dissertations

"The first part of this dissertation was aimed at studying the densification of ZrB₂ ceramics by pressureless sintering techniques. Various processes have been applied to coat ZrB₂ powders with polymer precursors, which were used to produce C after charring. After sintering at 1900⁰C, relative density increased of ~70% for uncoated ZrB₂ to >99% for ZrB₂ coated with at least 1.0 wt% C. Thermodynamic analysis suggested that C reacted with and removed oxide impurities (ZrO₂ and B₂O₃) that were present on the ZrB₂ particle surfaces, which promoted densification by minimizing grain coarsening"--Abstract, page iv.

Immobilization Of Radioactive Materials In Iron Phosphate Glass, Melissa G. Mesko

Doctoral Dissertations

"The current study investigates the feasibility of using iron phosphate glass for the immobilization of radioactive wastes considered incompatible with borosilicate glass. Wastes may be incompatible with borosilicate glass due to high phosphorus content (Hanford tank sludges), the presence of halides (CsCl and SrF₂ capsules), or large amounts of uranium (SNF).

Between 20 and 60 wt% Hanford tank sludge was vitrified with an iron phosphate glass at ≤ 1200°C in 1 hour. The chemical durability of iron phosphate glassy wasteforms was as good as, or better than a reference borosilicate glass (10^-9 g/cm²/min) in distilled water …

Toughening Mechanisms In Weak Matrix Ceramic Composites, Jowoong Ha

Doctoral Dissertations

"Tough behavior of ceramic matrix composites is closely related to the weak interface between fiber and matrix. The weak interfaces in composites have been provided by reducing the chemical bonding and the residual thermal stresses between constituents. A new way to introduce the weak interface by induced porosity or damaged zones, so called porosity toughening or damage toughening respectively, was proposed in this study to provide the rationale for guiding development of oxide/oxide composites. The existence of porosity toughening was examined by qualitative theoretical consideration and experiments. Porous oxide/oxide composites were fabricated using alumino-silicate fibers (Nextel 440) and magnesium alumino-silicate …

Bubble Formation, Movement And Distortion In Viscous Glass, Simon Cheng-Ping Wang

Doctoral Dissertations

"A study of bubble formation, movement and distortion in viscous glass is described. A glass rod containing an irregularly shaped hole is heated to a temperature at where the glass viscosity is low enough to let the hole form a spherical bubble. Spheration occurs as the bubble moves upward in the glass rod. At the proper time, the rising bubble is decelerated and brought to a stop by increasing the glass viscosity by slowly reducing the temperature. The entrapped bubble is then cut from the glass rod and heated again, if necessary, to a lower temperature, to reduce distortion of …

Studies Of Defect Structure And Oxidation-Reduction Behavior Of Undoped Lamno₃, Sr-Doped Lamno₃ And Mg-Doped Lamno₃, Jen-Ho Kuo

Doctoral Dissertations

"Undoped LaMnO₃, Sr-doped LaMnO₃ and Mg-doped LaMnO₃ showed reversible oxidation-reduction behavior. These perovskites can be excess, stoichiometric or deficient in oxygen content depending on the specific conditions. Under very reducing conditions these oxides will decompose into new phases. Phase stabilities for these oxides were determined. The results showed that both Sr and Mg doping caused the LaMnO₃ to dissociate at higher oxygen activities than for undoped LaMnO₃.

Defect models were proposed to interpret the TG results, in which metal vacancies are assumed for the oxygen excess condition and oxygen vacancies are assumed for the oxygen deficient condition. Thermodynamic properties were …

Oxidation Kinetics Of Polycrystalline Srtio₃ And Lacro₃, Chi-Kung Jerry Yu

Doctoral Dissertations

"The oxidation kinetics of polycrystalline SrTiO₃ and LaCrO₃ were determined by measuring the time and temperature dependence of the weight and conductivity change of reduced samples. A region of fast diffusion followed by a reduced diffusion tail was observed in the TGA measurements. This observation can be interpreted as the initial diffusion along the boundaries and then spreading out into the lattice. The absence of the tail in the conductivity measurements is due to the high electron and hole mobility at the boundaries. The electrical conductivity and TGA results on Nb-doped LaCrO₃ show that at low oxygen …

Dissolution Of Multi-Component Systems, Robin Ashley Murphy

Doctoral Dissertations

"The validity of ideal barrier layer diffusion kinetics was examined in the NaCl/KCl - glycerol and Al₂O₃-CaO-Al₂O₃-SiO₂/slag corrosion systems. Single crystals and dense polycrystalline plates of pure NaCl or KCl exhibit steady-state corrosion rates within 10%, of calculated theoretical values, while dense mixtures of the two salts corrode at rates higher than either pure material. The results are compared to the grooving phenomena of NaCl/KCl bicrystals.

Polycrystalline Al₂O₃ is shown to corrode at the same rate as single crystal sapphire at 1400°C in CaO-SiO₂-Al_{2 …}

Thermogravimetric And Electrical Conductivity Studies Of Mg-Doped Lacro₃ And La-Doped Srtio₃, Brian Keith Flandermeyer

Doctoral Dissertations

"Mg-doped LaCrO₃ and La-doped SrTiO₃ are perovskite compounds that display electrical conductivity which is a function of partial pressure of oxygen (po2). It has been proposed that acceptor-doped LaCrO₃ becomes highly resistive at low po2's due to ionic compensation of the acceptor-dopant present by oxygen vacancies. SrTiO₃ has been thought to absorb O₂ into a crystallographic shear structure and exsolve strontium vacancies which can then ionically compensate the La present and give a high resistance at high po2's.

Given these models, relationships between weight loss and conductivity vs. po₂ are developed for both these …

Chemical Corrosion Of Ag Films On Glass, Hyun Soo Park

Doctoral Dissertations

"The chemical corrosion of chemically, vacuum and sputter deposited Ag films on an aluminoborosilicate and a soda lime glass was investigated in wet HCl and saturated water vapor as a function of concentration, temperature and time. The higher corrosion resistance of chemically deposited Ag films in comparison to evaporated or sputtered Ag films is attributed to their lower microvoid density and higher adhesion strength. Ag films on the more chemically durable aluminoborosilicate glass had a higher corrosion resistance. Furthermore, films which received a moderate thermal annealing (80 to 140° C) or were deposited on a glass surface washed with HN0 …

Thermally Stimulated Polarization And Depolarization Current (Tspc/Tsdc) In Glass, Chi-Ming Hong

Doctoral Dissertations

"The feasibility of studying ionic motion in glass using thermally stimulated polarization (TSPC)/depolarization current (TSDC) techniques was investigated with 4Na₂O·96SiO₂ and 30PbO·70SiO₂ (mol%) glasses. The TSDC peaks in these glasses were dependent on glass composition and attributed to bulk polarization. The high temperature background TSPC is shown to be due to dc conductivity, whereas the TSPC/TSDC peaks in the 4Na₂O glass are attributed to shorter range Na⁺ motion.

The electrical conductivity of glasses determined by TSPC agrees well with that measured by conventional ac or dc techniques. The TSPC technique is a rapid and easy method of measuring the …