Master of Science, University of Toledo, 2024, Chemistry

Thermal expansion is a physical property that may contribute to materials' malfunctioning in applications ranging from various electronics to construction and other engineering fields. As heat is applied to or inherently generated by materials, they tend to expand, thereby causing stress, strain, cracks, and structural distortion at the interfaces between dissimilar materials. These structural misalignments, resulting from thermal expansion, adversely affect the properties of a material, which in turn leads to a change in a material's performance. This change in performance may disrupt the original purpose for which the material was made. These challenges make complementary materials that can reduce or eliminate the thermal expansion of other materials when incorporated into a composite attractive. Negative thermal expansion (NTE) materials are materials that contract upon heating. These materials can serve as fillers in composites to complement positive expansion materials and reduce overall thermal expansion in composite materials. Such composites can find applications in high precision optical mirrors, in the aerospace industry, in dental fillings, and ultimately, in various electronics. However, a thorough investigation of these promising materials is needed to understand some of the problems currently preventing full implementation. Among these challenges, avoiding temperature and pressure induced phase transitions that form positive expansion polymorphs has been an important factor. These phase transitions destroy the NTE property of the materials. Hence, stabilizing the NTE phase in a wider temperature and pressure range will enhance the materials' potential applications. This research focuses on the scandium tungstate (Sc2W3O12) family of NTE materials, represented as A2M3O12 (A = trivalent cation, M = tungsten, molybdenum). This family was chosen because of the wide range of cations that can be incorporated into the structure due to the chemical flexibil (open full item for complete abstract)

Committee: Cora Lind-Kovacs (Committee Chair); Michal Marszewski (Committee Member); Jon Kirchhoff (Committee Member) Subjects: Chemistry; Materials Science

Master of Science in Engineering Mechanics, Cleveland State University, 2024, Washkewicz College of Engineering

This paper presents a computational finite element analysis (FEA) focused on the utilization of shape memory alloy (SMA) interfaces as thermal expansion compensators for ductile positive coefficient of thermal expansion (CTE) materials such as Aluminum 6061-T6. The investigation delves into the efficacy of superelastic, one-way, and two-way shape memory effects in mitigating thermal expansion-induced stresses within engineering structures utilizing beam components. The research examines critical structural factors in a fixed beam system such as thermally induced internal stresses and buckling resilience at varying thermal loads. Computational simulation software from ANSYS Mechanical was calibrated to fit previous data from the literature on commercially available NiTi-based SMA properties. Comparing noninterface and SMA-interfaced beam structures, this study demonstrates the potential of SMAs to mitigate thermally induced stresses, thereby enhancing the structural integrity and longevity of engineering structures in thermal gradient environments. Furthermore, this paper proposes potential industries where the implementation of SMA interfaces could prove advantageous over current thermal compensating practices, including aerospace, optical, and civil engineering. This paper also introduces employing two-way shape memory alloys (TWSMAs) in thermal compensation by using computational and numerical analysis to showcase that TWSMAs response can be trained to perform similarly to materials with a negative thermal coefficient. By leveraging the unique property of trained TSMAs of the bidirectional shape memory effect, the aim was to demonstrate a second stress-free thermal state at an elevated temperature to increase the structure's buckling resilience. This research underscores the practical feasibility and performance of SMA interfaces as thermal expansion compensators, setting the stage for further exploration of advanced SMA technologies.

Committee: Josiah Owusu-Danquah (Committee Chair); Michael Gallagher (Committee Member); Stephen Duffy (Committee Member) Subjects: Aerospace Engineering; Civil Engineering; Engineering; Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy, University of Toledo, 2015, Chemistry

Research on control of thermal expansion of polymers has attracted significant attention, since polymers exhibit excellent mechanical and electronic properties, but suffer from high thermal expansion due to the thermal motion of their long molecular chains. Such problems can be addressed through formation of composites that contain an inorganic filler material. Filler materials reduce the thermal expansion of polymers through restriction of polymer chain motion. One particular area of interest is the introduction of negative thermal expansion (NTE) materials into polymer composites. The NTE property is expected to have an additional effect on the reduction of the coefficient of thermal expansion (CTE) of the composites. Several papers have demonstrated successful reduction of the CTE of polymer composites using cubic ZrW2O8, however, it is still unclear how much of this effect is caused by the NTE behavior, and how much is due to chain stiffening. To address whether the use of expensive NTE materials is justified, this project is designed to investigate the exact effects of NTE and chain stiffening on the reduction of thermal expansion of polymer composites. This objective was achieved through the preparation and testing of two sets of composites containing isomorphic particles with opposite thermal expansion (ZrW2O8 and ZrW2O7(OH)2¿2H2O), which possess identical chain stiffening effects. The first goal of the project was to synthesize two different particles that have identical morphology but opposite thermal expansion, with cubic ZrW2O8 as the NTE material of choice. The initial idea was to use a-Al2O3 (corundum), which has a known positive CTE value, as the second material. This phase can be obtained through heat treatment of AlOOH at about 1100 °C. The synthesis of AlOOH with controlled morphologies based on choice of synthetic conditions has been reported. Attempts on the synthesis of AlOOH were made through two different routes. Neither of them delivered par (open full item for complete abstract)

Committee: Cora Lind-Kovacs Ph.D. (Committee Chair); Maria Coleman Ph.D. (Committee Member); Jon Kirchhoff Ph.D. (Committee Member); Terry Bigioni Ph.D. (Committee Member) Subjects: Chemistry

Master of Science (M.S.), University of Dayton, 2021, Electro-Optics

The durability of thin film optical interference filters, integrated in systems ranging from imaging sensors to energy-efficient IR-blocking windows, is affected by its stress. The purpose of this work is to explore the thermal stress in thin films, the result of a contrast in the coefficient of thermal expansion (CTE) between the substrate and the film. While much research is focused on thin film intrinsic stress, thermal stress should also be considered for systems designed for high temperature variability and for systems where the film and substrate material properties vary greatly. This work characterizes the coefficient of thermal expansion and the Young's Modulus of SiO2 and Ta2O5 films, common low and high-index optical materials, along with composite SiO2-Ta2O5 thin films grown by reactive co-sputtering. A model for the variation of the CTE as a function of film composition is proposed, showing general agreement with the measured data. Characterization of the thermal stress in the film-substrate system is measured using a custom-built instrument, and the Young's Modulus is verified using nano-indentation. A method for evaluating the instrument noise, and its effect on the precision of the calculated CTE and Modulus values is characterized for this instrument. A model is proposed to enhance future designs-of-experiment using this instrument.

Committee: Andrew Sarangan (Advisor); Christopher Muratore (Committee Member); Jonathan Vernon (Committee Member); Lirong Sun (Committee Member) Subjects: Materials Science; Optics

MS, University of Cincinnati, 2019, Engineering and Applied Science: Mechanical Engineering

Topology optimization has gained widespread attention in the research and industrial community after the advent of Additive Manufacturing (AM). The nature of this manufacturing process made efficient building of parts with intricate geometries possible. Typically, parts used in aviation and aerospace applications are required to have less weight for fuel efficiency and higher load bearing capacity. To address this requirement, multi-material lattice structures with optimized material properties are designed. Topology optimization for optimized mechanical and thermal properties of the base cell of a lattice structure using multiple materials is the focus of the research reported in this thesis. A weighted multi-objective optimization model is defined to generate the unit cell. Volume constraints are defined with user-input volume fractions of individual material phases. Homogenization method is used to calculate the equivalent material property of the design domain comprising two materials (and void). A novel octant symmetry filter, and a prismatic density distribution filter is applied to generate lattice structures that does not require support structures while manufacturing using multi-material AM processes, specifically Directed Energy Deposition (DED). The unit cell of the lattice structure is optimized for high overall mechanical stiffness, low coefficient of thermal expansion, and low thermal conductivity. Two design examples are provided to show unit cells with and without the prismatic density filter. A Finite Element (FE) Analysis model is used to compare the deformations and nodal temperatures between the multi-material lattice structure and an equivalent design domain assigned with the homogenized material properties. The results from the FE analysis shows that the generated lattice structure and its computed effective material properties are accurate.

Committee: Sam Anand Ph.D. (Committee Chair); Manish Kumar Ph.D. (Committee Member); Kumar Vemaganti Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (PhD), Ohio University, 2017, Civil Engineering (Engineering and Technology)

Low-temperature cracking is a major pavement distress for asphalt pavements in most northern parts of the United States and other colder regions of the world. Pavements exposed to cold conditions are subjected to thermal stresses which can result in cracking when the induced stresses exceed the tensile strength. Local governments and road agencies spend large sums of money annually to repair defects in pavements caused by low-temperature cracking. Researchers need straightforward and routine test devices to characterize asphalt mixture's low-temperature performance in the laboratory. These tools are also required to design pavements that can perform satisfactorily in cold temperatures, and for the prediction of frequency and magnitude of cracks developed in asphalt pavements. The low-temperature performance characteristics of asphalt mixtures can be grouped into two broad components. There is the stiffness and thermal contraction component which accounts for the magnitude of strains or stresses induced in the mixture during cooling. The strength or fracture toughness component accounts for the ability of the mixture to resist the induced stresses and to prevent cracking. The main objective of this dissertation was to develop straightforward and routine tests devices for low-temperature characterization that would account for these two components of mixture's low-temperature performance. The Ohio Coefficient of Thermal Contraction (CTC) device developed as part of this dissertation was shown to produce repeatable test data. Asphalt mixture thermal strains recorded from the CTC device fitted the Bahia-Anderson CTC mathematical model for mixtures with a coefficient of determination (R2) greater than 0.999. Mixture properties such as binder grade, binder content, aging and the inclusion of recycled materials [Recycled Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS)] resulted in a significant change in the CTC. Asphalt mixtures prepared with two aggrega (open full item for complete abstract)

Committee: Kim Sang-Soo Dr. (Advisor); Nazzal Munir Dr. (Committee Member); M. Sargand Shad Professor (Committee Member); Masada Teruhisa Professor (Committee Member); Mark McMills Dr. (Committee Member); Yu Xiong Dr. (Committee Member) Subjects: Civil Engineering; Engineering; Geotechnology

Doctor of Philosophy, The Ohio State University, 2010, Industrial and Systems Engineering

Glass has been fabricated into different optical elements including aspherical lenses and freeform mirrors. However, aspherical lenses are very difficult to manufacture using traditional methods since they were specially developed for spherical lenses. On the other hand, large size mirrors are also difficult to make especially for high precision applications or if designed with complicated shapes. Recently developed two closely related thermal forming processes, i.e. compression molding and thermal slumping, have emerged as two promising methods for manufacturing aspherical lenses and freeform mirrors efficiently. Compression molding has already been used in industry to fabricate consumer products such as the lenses for digital cameras, while thermal slumping has been aggressively tested to create x-ray mirrors for space-based telescopes as well as solar panels. Although both process showed great potentials, there are a quite few technical challenges that prevent them from being readily implemented in industry for high volume production. This dissertation research seeks a fundamental understanding of the thermal forming processes for both precision glass lenses and freeform mirrors by using a combined experimental, analytical and numerical modeling approach. First, a finite element method (FEM) based methodology was presented to predict the refractive index change of glass material occurred during cooling. The FEM prediction was then validated using experimental results. Second, experiments were also conducted on glass samples with different cooling rates to study the refractive index variation caused by non-uniform cooling. A Shack-Hartmann Sensor (SHS) test setup was built to measure the index variations of thermally treated glass samples. Again, an FEM simulation model was developed to predict the refractive index variation. The prediction was compared with the experimental result, and the effects of different parameters were evaluated. In the last phase of this (open full item for complete abstract)

Committee: Allen Y. Yi PhD (Advisor); Jose Castro PhD (Committee Member); Betty L. Anderson PhD (Committee Member) Subjects:

Master of Science in Chemistry, Cleveland State University, 2011, College of Sciences and Health Professions

Three experiments were performed to demonstrate that thermal analysis is an important tool for use in colleges and universities for conducting scientific research. The first experiment used thermogravimetry, differential scanning calorimetry and thermal mechanical analysis to compare polymer resins from two ResinKits®, one from 1994 and the other from 2010. Analysis was done to determine if resins from the 1994 kit were viable standards. The experiments showed significant thermal differences between select resins and it was concluded that resins form the 1994 ResinKit® are no longer acceptable as standards. The second experiment used thermogravimetry and differential scanning calorimetry to determine the concentration of bound and un-bound water in commercial and generic samples of milk of magnesia. Those thermal methods were compared to traditional methods and it was determined that thermogravimetry was best suited for determining bound water and that differential scanning calorimetry revealed thermal differences that none of the other thermal techniques could detect. In the third experiment, four chemically similar aldohexose monosaccharides were evaluated using thermogravimetry to determine if the thermal analytical technique was sensitive enough to differentiate between the four monosaccharides. It was determined that thermogravimetry could detect differences between two groups of monosaccharides, but not between each monosaccharide individually. The result of these experiments clearly shows that thermal analysis is a valuable tool for scientific research and needs to be included more as part of the curriculum for chemistry students and not delegated as a “niche” study of only limited value.

Committee: Alan T. Riga PhD (Committee Chair); Bin Su PhD (Committee Co-Chair); Tobili Sam-Yellowe PhD (Committee Member) Subjects: Analytical Chemistry

Master of Science in Engineering, Youngstown State University, 2018, Department of Civil/Environmental and Chemical Engineering

The incorporation of additive manufacturing (AM) enables the ability to fabricate composite tooling molds rapidly and in a cost effective manner. This work has demonstrated the practice of an additive technology for manufacturing composite processing tools. In particular, this work has addressed tooling that is functional in the range of autoclave temperatures around 180°C. This has led to the use of Invar and ceramic materials for use in composite molding tools because of their relatively low coefficient of thermal expansion (CTE) performance, which is in range to that commonly displayed by carbon fiber reinforced composites during their solidifying curing process. In this project, three main approaches have been considered. The first innovative approach was based on printing a mold based on silica sand and infiltrating it with a polymer to yield a robust ceramic composite tooling. The second approach investigated the use of binder jetting to 3D print sand molds to cast molten Invar to produce the composite tooling. Indeed, 3D sand printing offers the ability to cast complex geometries without the geometric limitations associated with conventional pattern making. An additional technology using a Hybrid Direct Energy Deposition (DED) System for cladding Invar upon a steel molding structure has also been considered for producing potential composite tooling. Indeed, this unique approach could represent a promising technology for producing low cost composite tooling since only a small layer of Invar would be cladded to a non-expensive substrate. The results have shown that the aforementioned processes have successfully resulted in low CTE composite tooling molds. This work presents innovative AM processes by initially investigating additive manufacturing processes for composite tooling.

Committee: Pedro Cortes PhD (Advisor); Brett Conner PhD (Committee Member); Jason Walker PhD (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 2017, Mechanical Engineering

Objective of this thesis is to investigate the impact of point defects on thermal conductivity and lattice expansion in uranium dioxide ceramic. Specific emphasize is on light ion irradiation induced point defects which causes the degradation of thermal conductivity of oxide ceramics. Radiation induced defects include vacancies and interstitials hosted by the anion and cation sub lattice of the structure. A crystallographic structure is assumed for each defect and is used to model defect impact on lattice parameter. In ceramic materials, thermal conductivity is governed by phonon modes determined by crystalline structure. The irradiation induced point defects limit thermal transport by acting as phonon scattering centers. The point defects scattering originates from both the mass and ionic radius mismatch between the impurity atom and the host lattice. We present a model to estimate the phonon scattering parameter for different types of point defects and implement it in classical phonon mediated thermal transport model to estimate the thermal conductivity reduction in light ion irradiated UO2. The results are compared to results of experimental measurements. Laser based modulated thermoreflectance (MTR) technique was used to measure the thermal conductivity model in ion irradiated UO2 samples. Unlike laser flash analysis, traditionally used for measuring thermal conductivity in nuclear materials, MTR method has a sensitivity to a few micron thick thin damage resulting from ion beam irradiation. In this technique, the irradiated sample, coated by a thin metallic film, is heated by a harmonically modulated laser pump and a probe beam measures the temperature induced changes in reflectivity. In this work, experimentally measured thermal wave phase profiles obtained from UO2 samples irradiated with 2.6 MeV H+ ions were analyzed using different multilayer approximations of the damaged region. An infinite damage layer approximation model that neglects undamaged layer (open full item for complete abstract)

Committee: Marat Khafizov Dr. (Advisor); Sandip Mazumder Dr. (Committee Member) Subjects: Materials Science; Mechanical Engineering; Nuclear Engineering; Nuclear Physics

PHD, Kent State University, 2015, College of Arts and Sciences / Chemical Physics

Topological defects plays an important role in many physical processes ranging from morphogenesis of phase transitions in condensed matter system to the response to surface confinement and application of external fields. In this dissertation, we investigate the topological defects both in lyotropic and thermotropic nematics in order to characterize the studied materials.

Committee: Oleg Lavrentovich (Advisor); Hiroshi Yokoyama (Committee Member); Liang-Chy Chien (Committee Member); Samuel Sprunt (Committee Member); Elizabeth Mann (Committee Member) Subjects: Engineering; Experiments; Materials Science; Optics; Physical Chemistry; Physics

Master of Science, University of Toledo, 2015, Chemistry

Negative thermal expansion (NTE) materials have attracted considerable research interest in recent decades. These unique materials shrink when heated, offering a potential means to control the overall thermal expansion of composites. Several families of materials display this behavior, the largest of which is the A2Mo3O12 family (also called the scandium tungstate family), in which A is a trivalent cation and M is molybdenum or tungsten. These materials show NTE in an orthorhombic structure, but many members transform to a monoclinic structure with positive expansion at low temperatures. Many properties of these materials are dependent on their elemental composition, especially the identity of the A3+ cation. This includes the magnitude of NTE, as well as the phase transition behavior as a function of temperature and pressure. It is also possible to create "mixed site" cation A2Mo3O12 materials, in which the A site is occupied by two different cations. These are described as AxA'2-xM3O12 materials, as the composition A:A' can vary. Creating these new compositions may result in different phase transition properties or the ability to tune the NTE properties of these materials. In this work, the focus was on synthesis and characterization of indium gallium molybdate (InxGa2-xM3O12). The non-hydrolytic sol-gel (NHSG) method was used to synthesize indium gallium molybdate while exploring a variety of reaction parameters. While the goal was to create stoichiometric, homogenous materials, it was found that this could not be accomplished using easily accessible parameters during NHSG reactions. However, it was discovered that certain conditions allowed unusually low temperature (230 °C) crystallization of these materials. Similar conditions were explored for single cation A2Mo3O12 materials, and it was determined that crystallization of indium molybdate, iron molybdate, and scandium molybdate was possible at temperatures of 230 or 300 °C. This extremely low temperature (open full item for complete abstract)

Committee: Cora Lind-Kovacs PhD (Committee Chair); Eric Findsen PhD (Committee Member); Jon Kirchhoff PhD (Committee Member) Subjects: Chemistry; Materials Science

Master of Science, The Ohio State University, 2014, Mechanical Engineering

Smart materials are a class of materials that couple different regimes, such as thermal, mechanical, electrical, and magnetic. Shape memory alloys (SMAs) are classified as such due to their ability to couple the thermal and mechanical regimes. One particular type of SMA is nickel-titanium (NiTi), which can recover up to 8\% elastic strain. In this study, the large strain recovery of NiTi is used in the development of a metal matrix composite that exhibits low to near-zero coefficient of thermal expansion. This is done by utilizing the strain recovery of NiTi fibers to offset the expansion of the aluminum matrix in which they are embedded. The fabrication of this metal matrix composite is made possible through the use of ultrasonic additive manufacturing (UAM). Ultrasonic additive manufacturing combines ultrasonic welding with subtractive machining operations to create complex parts from dissimilar metals. The resulting parts can be made of similar or dissimilar materials. In UAM, 20kHz vibrations created by piezoelectric transducers are transferred to a textured steel horn, which presses a thin strip of metal to a substrate with a normal force in excess of 5000 Newtons. Under these conditions, the surface oxides and asperities are broken down, producing atomically clean faces on both pieces, allowing for pure metal-to-metal contact and instantaneous bonding to take place. Unique to UAM is its low-temperature, solid-state operation, which means no melting of the constituent materials takes place. This feature provides the unprecedented opportunity to embed materials that are thermally sensitive, such as SMAs. This study focuses on the fabrication and characterization of NiTi-Al UAM composites with an emphasis on developing a method of producing composite structures. Process parameters that were studied include securing the NiTi ribbons during fabrication, ensuring proper placement of the ribbons in the composite, and applying the necessary pre-stress to produce (open full item for complete abstract)

Committee: Marcelo Dapino PhD (Advisor); Mark Walter PhD (Committee Member) Subjects: Engineering; Mechanical Engineering

MS, University of Cincinnati, 2003, Engineering : Civil Engineering

Three types of fiber reinforced polymer bridge deck panels were supplied to the University of Cincinnati. Specimens included were small-size specimens supplied by their respective manufacturers and full-size specimens obtained from the Salem Avenue bridge in Dayton, Ohio. Research performed includes: long-term environmental monitoring, load testing, and finite-element analysis. Long-term environmental monitoring was performed on small-size specimens for all three deck types. Environmental monitoring included collection of temperature and strain data over a period of nine months. Average internal mperature, coefficient of thermal expansion (in both directions), and temperature gradient were calculated for each type of panel. Load testing was performed at the University of Cincinnati Large Scale Test Facility (UCLSTF). Load tests were performed on small-size specimens and full-size specimens obtained from a bridge retrofit project. Effective flexural and shear stiffness were calculated for each panel tested. Failure load and failure type for each test are reported. Finally, a finite-element model of a full-size panel was created for one of the deck types in order to capture the effects of internal damages. Analysis results of the finite-element model are compared against experimental results.

Committee: Dr. Bahram Shahrooz (Advisor) Subjects: Engineering, Civil

Master of Science in Mechanical Engineering, University of Toledo, 2011, Mechanical Engineering

Composite materials are being more frequently used in a wide variety of industries. Their high strength to weight ratio makes them a desirable material in many applications. In some specific cases, polymer based composites can be subjected to large changes in temperature causing undesirable amounts of expansion. To reduce the composite's thermal expansion, materials that have negative coefficients of thermal expansion are used as a filler material. Zirconium tungstate (ZrW2O8) is a metal oxide which exhibits thermal behaviors not seen in most other materials. When subjected to a positive temperature change, ZrW2O8 will decrease in volume as opposed to most other materials which show an increase in volume. This makes ZrW2O8 an ideal candidate to be used as filler material in these polymer composites to reduce their overall thermal expansion. While experimental research on ZrW2O8 composites has previously been completed, this research looked at the finite element modeling of these composite materials and tried to gain a better understanding of their possibilities. Initial two-dimensional models were created using COMSOL Multiphysics with basic geometries for both the matrix and filler. The results from these tests showed that the filler geometry had little effect on the expansion results and volume fraction was the most important factor. To further test this, more complex models were created using three-dimensional geometries with the same volume fractions. These results confirmed the findings of the two-dimensional tests by showing similar expansion. These results were then compared to published experimental data where it was found that all the models showed less expansion than the physical experiments of the same volume fraction. The difference between the finite element analysis (FEA) and experimental results was attributed to the interaction between the filler and matrix materials. In the models, the bond between the two was considered perfect, with no voids or se (open full item for complete abstract)

Committee: Dr. Lesley M. Berhan (Committee Chair); Dr. Maria R. Coleman (Committee Member); Dr. Yong X. Gan (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

Master of Science, University of Toledo, 2011, Chemistry

In recent years, negative thermal expansion (NTE) materials have become of increasing interest. These materials contract upon heating, and have potential for achieving better control of thermal expansion in composite materials. By using an NTE compound as a filler material into these composites, it is possible to offset the positive thermal expansion of other components in the composite. As a result, these NTE materials can find use in a wide range of applications such as optics, polymers, electronics, tooth fillings and any other area where exact positioning of parts over a wide range of temperatures is crucial. One of the most popular NTE materials is cubic ZrW2O8. Thermodynamically stable zirconium tungstate was first synthesized in the 1950's through traditional solid state methods. It was only recent that the metastable phases could be achieved through low temperature methods, that involves conversion of a precursor material ZrW2O7(OH)2•2H2O to cubic ZrW2O8. Through hydrothermal synthesis, previous work on ZrW2O7(OH)2•2H2O showed exceptional particle and morphology control with use of alcohols/HCl, which is desirable for optimal composite integration. It was recently discovered that ZrW2O8 particles obtained through this synthesis route had reduced stability in atmosphere. The instability was linked to autohydration that changed the properties of the material resulting in weak positive thermal expansion. Interestingly, nanosized ZrW2O8 obtained hydrothermally in perchlorate/NaCl with the absence of alcohols show very limited autohydration; however this is a non-preferred synthesis route due to high agglomeration levels. Reported autohydration on mixed ZrMoxWx-1O8 solid solutions by Sleight et al. provided a logical defect driven explanation for the cubic ZrW2O8 nanoparticles. Detailed investigation was performed on cubic ZrW2O8 hydrothermally obtained by the alcohol/HCl synthesis pathway. An understanding of what is causing autohydration was discovered through (open full item for complete abstract)

Committee: Cora Lind PhD (Advisor); Jon Kirchhoff PhD (Committee Member); Jared Anderson PhD (Committee Member) Subjects: Chemistry; Materials Science

Doctor of Philosophy, University of Toledo, 2010, Chemistry

In recent years, there has been an increased interest in negative thermal expansion(NTE) materials, which contract upon heating. Materials exhibiting this property have the potential for achieving better control of thermal expansion through the synthesis of composite materials with more desirable expansion coefficients. By introducing NTE materials into these composites, it is possible to offset the positive thermal expansion of other components in the composite. As a result, these NTE materials can find use in a wide range of applications such as optics, electronics, tooth fillings and any other area where exact positioning of parts over a wide range of temperatures is crucial. A family of materials that has been known to show NTE are A2M3O12 compounds, where A can be a variety of trivalent cations and M can be Mo or W. Previous work on this system has shown that the thermal expansion is highly dependent on the type of trivalent cation employed. However, in spite of the interest in these 2M3O12 compounds, little research has been dedicated to synthesizing materials containing two aliovalent cations instead of just one or two trivalent cations. In fact, the first example of a heterosystem with +2 and +4 cations was not reported until 2004. This dissertation presents results of investigation and characterization of these mixed cation systems, and the change in the thermal expansion properties. The first goal of the research presented herein was to synthesize mixed cation systems using a lower temperature route, and then compare the materials synthesized using low temperature methods with those synthesized using the ball-milling method.This will ensure the validity of applying a lower temperature method to these mixed cation systems. A non-hydrolytic sol-gel (NHSG) method was used, which is based on the reaction of metal alkoxides with metal halides to form M-O-M linkages, with alkyl halides as byproducts. With this method, MgHfW3O12 and MgZrW3O12 were successfully sy (open full item for complete abstract)

Committee: Cora Lind (Committee Chair); Eric Findsen (Committee Member); Jon Kirchhoff (Committee Member); Scott Lee (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Toledo, 2008, Chemistry

Negative thermal expansion (NTE) describes materials that shrink when they are heated. Most materials expand when heated displaying positive thermal expansion coefficient. Several oxide families display negative thermal expansion behavior. Recently, it has been shown that NTE materials can be used to reduce thermal expansion,and to achieve a more desirable expansion coefficient α, when incorporated into composites. In general, thermal expansion varies for every material. Therefore, problems may arise when attempting to bond multiple materials for applications if the thermal expansion coefficients differ significantly. Such a mismatch in thermal expansion may result in stresses, cracks, or separation at the interface. This can cause inefficiencies, and even device failures. Preparation of composite materials containing NTE oxides should allow increased control over thermal expansion to produce better matches while preserving the properties of the original matrix. NTE is commonly found in the A2M3O12 family (A=trivalent metal; M=W, Mo). These materials crystallize in an orthorhombic unit cell, and their α-value is highly dependent on the identity of the cations (A3+ and M6+). Some compositions show a phase transition to a monoclinic structure with α>0 at low temperatures. Literature suggests that the magnitudes of NTE, as well as the crystal structure and phase transition temperatures, are affected by cation substitution. However, current theories only apply to a small number of these compounds. This research explores the various factors that influence the behavior of this oxide family of materials. When examining the influence of cation substitution on thermal expansion and phase transition behavior, synthesis of compounds using traditional solid-state methods limits the number of cations that can be incorporated into this structure. To overcome these limitations, a non-hydrolytic sol-gel (NHSG) method was used during preparation of the mixed metal compounds. The N (open full item for complete abstract)

Committee: Cora Lind PhD (Advisor); Amanda Bryant-Friedrich PhD (Committee Member); Jon Kirchhoff PhD (Committee Member); Mark Mason PhD (Committee Member) Subjects: Chemistry

Master of Science, The Ohio State University, 2012, Mechanical Engineering

Solid oxide fuel cells (SOFCs) are electrochemical energy conversion devices capable of producing electrical power with high efficiency and low emissions. SOFCs are characterized by ceramic electrolyte membranes which transport oxide ions in the range of temperatures between 600°C and 1000°C. In order to facilitate efficient, low-range temperature operation the electrolyte is typically made very thin, on the order of 40 µm. SOFCs also employ porous electrodes on either side of the electrolyte which are then placed in contact with current collectors and seals. In the fuel cell environment, with high temperatures, substantial thermal gradients, mechanical loading between layers, as well as the desire to be able to thermally cycle the cell, one of the layers or components must provide mechanical support. It is typical for either the anode or electrolyte to provide the necessary mechanical support. This thesis focuses on an electrolyte that is used for electrolyte-supported SOFC configuration. To address the need for mechanically robust electrolytes, NexTech Materials has developed the FlexCellTM electrolyte. This electrolyte design incorporates 40 µm thick conducting regions in a honeycomb pattern, and surrounding 200 µm thick stability regions. Various experiments on and determinations about this material and design must be made to ensure sufficient mechanical stability during fuel cell operation. Thermal stresses from high temperatures, temporal and spatial temperature gradients, and differential thermal expansion of contacting materials, are critical issues within SOFCs. The critical property related to these issues, coefficient of thermal expansion (CTE), was measured in this work. An apparatus to measure the CTE of the FlexCellTM electrolyte material was designed and implemented. The average CTE of 3 mol% Y2O3-ZrO2 (yttria stabilized zirconia or 3YSZ) was found to increase from 9 µm•m-1•°C-1 between room temperature (RT) and 180°C to nearly 11.5 µm•m-1•°C-1 from R (open full item for complete abstract)

Committee: Dr. Mark E. Walter (Advisor); Dr. Brian D. Harper (Committee Member) Subjects: Materials Science; Mechanical Engineering

Master of Science (MS), Ohio University, 2001, Civil Engineering (Engineering)

Effects of thermal expansion on a skewed semi-integral bridge.

Committee: Eric Steinberg (Advisor) Subjects: Engineering, Civil