Doctor of Philosophy, Case Western Reserve University, 2013, Chemical Engineering

A new class of high-performance resins combining the molecular structure of both traditional phenolics and benzoxazines is developed. The monomers are synthesized through Mannich condensation reaction of methylol-functional phenols and primary amines, in the presence of paraformaldehyde. The network structure is built utilizing simultaneous addition and condensation polymerization through benzoxazine and resole chemistry. The presence of methylol groups accelerates the polymerization with improved thermal properties of the produced polymer. The polymers show high glass transition temperature, Tg (274-311°C) and excellent thermal stability compared to the traditional polybenzoxazines. The non-isothermal DSC analysis using Kissinger and Ozawa methods show that polymerization reactions of methylol monomer exhibits lower apparent non-elementary activation energy (83.6 and 93.5 KJ/mol) compared to the unfunctionalized monomer (94.1 and 101.4 KJ/mol). The thesis shows an optimum solution to overcome the historic limitations of using phenolic/urethane materials. The limitations include the slow reaction kinetics of the isocyanate and phenolic compounds along with poor thermal stability of the produced urethane linkages. The new approach is based on reacting methylol benzoxazines with isocyanates and polyols to form polybenzoxazine/polyurethane copolymers. The incorporation of benzoxazine in the copolymer shifted the decomposition temperature to (285-300 °C) with char yield of (18-53%), depending on the benzoxazine content. In addition, the thesis deals with the preparation of high thermally conductive coating for electronic components. For this purpose, boron nitride nanosheet (BNNS) is used as a model system to be dispersed in benzoxazine monomer. Composite of the commercial BN embedded into methylol benzoxazine monomer was used as a control. BNNS systems exhibit higher thermal conductivity values than the BN systems. The SEM images show that dispersion and distributio (open full item for complete abstract)

Committee: Syed Qutubuddin Dr. (Advisor); J. Adin Mann Dr. (Committee Member); R. Mohan Sankaran Dr. (Committee Member); David Schiraldi Dr. (Committee Member) Subjects: Chemical Engineering

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

Two limitations of polymeric fiber reinforced composite materials are their susceptibility to damage, and their reduced thermal conductivity compared to metals. This thesis proposes techniques to address these limitations and to make composite materials more multi-functional and reliable like metals. Laminated composites are prone to damage due to impacts which cause localized delamination and microcracking. It is challenging to detect these types of damages because non-destructive inspection takes the structure out of service, inspection is slow and expensive on large structures, and the damage may not be obvious on the outer surface. Left undetected, the damage can propagate due to loading during normal use and lead to reduced performance or failure of a component or the entire structure. In most applications, detection of these internal damages is critical to maintain the performance and structural integrity of components, and to assure the safety of the aircraft or wind turbine. Composites are used because they are lightweight and corrosion resistant, but must be over-designed to account for possible undetected damage which increases cost and weight. Structural Health Monitoring (SHM) is an approach to continuously monitor structures for damage while they are in operation. The complexity and cost of monitoring large structures where damage can occur anywhere on the structure has so far restricted the application of SHM systems. This thesis presents a method to monitor large composite structures for damage using a simple and reliable approach. Carbon Nanotube (CNT) sheets are used as sensors to detect internal damages in composites. Two CNT sheets separated by a dielectric form the sensor. Impact damage can short circuit the two CNT layers indicating that damage has occurred. Since CNTs have good electrical and thermal conductivity, they will improve the thermal conductivity of composites. Through the thickness thermal conductivity of CNT sheet is characterize (open full item for complete abstract)

Committee: Mark Schulz Ph.D. (Committee Chair); Jude Iroh Ph.D. (Committee Member); Ashley Paz y Puente Ph.D. (Committee Member) Subjects: Materials Science

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 in Polymer Engineering, University of Akron, 2010, Polymer Engineering

Boron Nitride (BN) is widely used in thermal management applications involving thermoplastic polymeric articles. BN platelet agglomerates give higher through-plane thermal conductivity and more isotropic thermal conduction than single crystal powder grades. However, the agglomerates are relatively weak and susceptible to attrition when subjected to aggressive shearing in processing flows. Thus, it is imperative that compounding of BN with polymer and subsequent processing of the compounds should be carried out below a critical shear stress level in order to preserve the agglomerate structures and to obtain isotropic thermal conduction. This study focuses on identification of the critical hydrodynamic stress level for BN agglomerate attrition and its effect on the thermal conductivity of the composites produced by extrusion compounding and injection molding. Two agglomerate grades of BN viz. PT350 and CF400 with different mean particle sizes were used as fillers in polycarbonate (PC) at different filler loadings. Shear experiments were carried out in rotational and capillary rheometers and the status of BN particle breakdown was analyzed using Scanning Electron Microscopy (SEM) images. The results of shear experiments in rheometric flows revealed that morphology of BN particles and thermal conductivity of the composites strongly depended on the shear stress encountered. The particle size distribution and thermal conductivity measurements revealed that considerable breakage of agglomerates occurred during extrusion and injection molding which affected through plane conductivity of the composites. The in-plane conductivity was seen to increase with injection speed due to particle orientation during injection molding. The in-plane thermal conductivity as high as 2.47 W/mK around twelve times higher than neat polycarbonate was obtained with 35 wt% loading of boron nitride. It was also found that polycarbonate filled with 35 wt%PT350 and 25 wt% CF400 showed an increase in (open full item for complete abstract)

Committee: Sadhan Jana Dr. (Advisor) Subjects: Polymers

Doctor of Philosophy, The Ohio State University, 2024, Chemistry

The design of next generation electrical and thermal transport materials is of far-reaching importance for myriad applications from thermoelectrics to dynamic transport switching. To that end, axis-dependent conduction polarity and thermal-switching materials hold significant promise. Axis-dependent conduction polarity (ADCP) is a phenomenon in which the electrons (n-type carriers) and holes (p-type carriers) are preferentially conducted along orthogonal directions in a crystal. The driving force for this phenomenon is a large (> 10x) anisotropy in the electron and hole mobilities between orthogonal directions. Herein is discussed the development of the first air-stable, wide bandgap (> 0.4 eV) semiconductor that displays ADCP, orthorhombic PdSe2. The anisotropy in the hole mobilities between the cross-plane and in-plane directions is > 100x, with holes preferentially conducting along the cross-plane direction. Additionally, the onset temperature of ADCP can be controlled via extrinsic doping with Ir and Sb as p-type and n-type dopants, respectively. When the chemical potential is near the valance band (Ir doping), ADCP is not observed up to 400 K. When it is mid-gap the onset temperature is about 350 K. But when it is near the conduction band (Sb doping), the onset temperature can be as low as 100 K. The dopant dependent onset temperature indicates the necessity for both the conduction and valance bands to be populated sufficiently to observe ADCP. Studies in this model system pave the way for further ADCP studies in semiconductors. Solid-state thermal switching is the rapid and reversible control over the thermal conductivity of a material between some low and high value without the need for physical phase changes or moving parts. Topologically non-trivial materials are promising candidates for solid-state thermal switching on account of their anomalous transport properties. Therefore, EuCd2As2 and MnBi2Te4 were studied for their thermal switching potential. Eu (open full item for complete abstract)

Committee: Joshua Goldberger (Advisor); Christine Thomas (Committee Member); Patrick Woodward (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2023, Materials Science and Engineering

This thesis reports experimental data on the transport properties of ferroelectric and ferromagnetic solids, as well as topological insulators. The analogies between the thermal perturbations of ferroelectric and ferromagnetic order are explored from a fundamental point of view. While ferromagnetic order is the object of an established field of study, spin caloritronics, the study of perturbations in ferroelectrics stands to establish a new field, polarization caloritronics. This new field, following in the footsteps of its predecessor, has the potential to impact thermoelectricity, heat controlling devices and possibly phonon-based logic. The first subject of this dissertation is a new quasiparticle, the ferron, defined as the elementary thermal excitation of polarization in a ferroelectric material. Likening the ferron to the quantum of a spin wave, the magnon, we measured the ferronic thermal conductivity in lead zirconium titanate (PZT), a well-established ferroelectric material. With the assistance of resonant ultrasound spectroscopy (RUS) to establish the electric field dependent sound velocity, we determined that optical phonons hybridize with acoustic phonons assisting in the formation of a polarization-lattice coupled phonon, coined the ferron. The ferron theory states that the electric field dependent sound velocity and thermal conductivity can be predicted with three material properties: the Gruneisen parameter which quantifies the anharmonicity of the phonon dispersion with respect to volume changes, and d33 and d31, which are the piezoelectric coefficients which quantify the parallel and perpendicular strain of the system in an electric field, respectively. The predicted field dependency using published values for PZT agreed well with our observations. To further test this theory, we performed RUS and thermal conductivity measurements on a relaxor ferroelectric, a solid solution of lead magnesium niobate and lead titanate (PMN-PT). Here, the theory (open full item for complete abstract)

Committee: Joseph Heremans (Advisor); Wolfgang Windl (Committee Member); Roberto Myers (Committee Member); Patrick Taylor (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2022, Nuclear Engineering

Molten salts have favorable properties for advanced energy systems, including thermal energy storage, molten salt nuclear reactors, concentrating solar power systems, and fusion reactors. However, uncertainties and knowledge gaps exist in many molten salts' chemistry, thermophysical properties, and thermodynamics. The thermal conductivity of molten salt is relatively lacking in experimental data and features high uncertainties and discrepancies in the existing experimental data. The limited knowledge of molten salt thermal conductivity inhibits the development of new technologies that can utilize molten salt. Thus, there is a need for improved understanding and standardized experiment techniques to provide the property data critical for these applications. To address this need, a steady state variable gap thermal conductivity measurement system was designed, fabricated, and tested on high-temperature helium and nitrate salt. The tests showed reasonable agreement with the standards but showed increasing error with increasing temperature. The design was considered suitable for further development and testing, but additional modifications to limit the effects of heat losses through the structure were required. A modified system was used to measure eutectic LiF-NaF-KF molten salt. This salt mixture has discrepancies between existing data sets and shows a positive trend of thermal conductivity with temperature, which disagrees with current theoretical predictions and the behavior seen in many other salt mixtures. The experimental results were compared to a kinetic theory-based (Gheribi) thermal conductivity model and molecular dynamics predictions to validate the models. The experimental data were found to agree with the models, showing a negative dependence of thermal conductivity with temperature for the first-time using experiments leading to further investigation of the Gheribi model in the subsequent studies. The Gheribi model assumes that density, which s (open full item for complete abstract)

Committee: Lei Cao (Advisor); Vaibhav Sinha (Committee Member); Tunc Aldemir (Committee Member); Lei Cao (Committee Chair) Subjects: Nuclear Engineering

Doctor of Philosophy, The Ohio State University, 2022, Mechanical Engineering

The realization of next-generation quantum-based computing and communication devices is dependent upon the advancement in thermal management. These challenges include but are not limited to sub-Kelvin temperature cooling for quantum computing and sensing and high-density thermal energy dissipation for electronics. Thermal circuit designs are limited by the conventional passive thermal components, such as thermal resistors and thermal capacitors, in contrast to a wide range of active components in the electrical domain. On the verge of the second quantum revolution, the development of materials that enable active switching of thermal transport in a wide range of temperatures and methods that provide advantages over current thermal management approaches are essential. In this thesis, I will introduce new mechanisms for controlling thermal transport in solids based on quantum phenomena. Only recently was it recognized that topological properties of electrons in certain solids can have a dominant impact on the equations of motion of electrons. We discovered an ideal Weyl semimetal system, a topological material, that is field-induced: Bi1-xSbx, with x varying from 0.04 to 0.22. We developed a theory for the topology-induced mechanism for the transport of heat by electrons, the thermal chiral anomaly, and experimentally proved its existence. Under the right conditions, the electronic thermal conductivity of a Weyl semimetal will increase linearly with the applied magnetic field. Secondly, we investigated the effect of Bose-Einstein condensation of excitons, an electron-hole pair, on the lattice thermal conductivity of an excitonic insulator. Our data showed a surprisingly high low-temperature thermal conductivity in Ta2NiSe5, an excitonic insulator, compared to those in Ta2NiS5, a conventional insulator with a similar lattice structure. We postulated the enhancement in thermal conductivity is due to the coupling of exciton condensate to the lattice. In the last chapt (open full item for complete abstract)

Committee: Joseph Heremans (Advisor); Joshua Goldberger (Committee Member); Sandip Mazumder (Committee Member); Nandini Trivedi (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2020, Mechanical Engineering

Thermal management is critical for both nuclear and electronics industry because of heat generation during the operation. Major part of energy consumed in microelectronic devices and nuclear reactors dissipates as heat, and sometimes also creates hot spots. This is critical and precarious for the nuclear applications, while for the electronics, it has detrimental effects on the device performance and affects the reliability of devices. The microelectronic devices and nuclear materials are exposed to the extreme environments such as irradiation, vacuum, and molten salts etc. In addition to the already existing intrinsic defects, this exposure leads to the creation of multiple defects inside the materials. The goal of this research is to understand the phonon transport physics at these small length scales due to intrinsic and extrinsic defects in the material. Primarily, three different materials are discussed in this report. SiC and sapphire have been chosen for their applications in both microelectronic devices and nuclear industry while ceria has been studied as a surrogate material for the nuclear fuels (UO2 and ThO2). There are different kinds of defects created inside the material when exposed to irradiation. The complex interaction of phonons with these defects dictates the resultant thermal transport however, it is difficult to apportion the impact of a particular type of defect. The approach used here employs materials induced with only a few types of defects at a time in order to isolate and study the impact of induced defect on thermal transport. Consequently, irradiation has been used in this study to induce desired defects inside the material and thereafter study their effect on thermal conductivity. Interstitials and vacancies, collectively known as point defects are formed under low dose and heavy ion irradiation regime. Here, SiC is irradiated using Kr ions to study impact of point defects on its vibrational and thermal properties. While th (open full item for complete abstract)

Committee: Marat Khafizov Prof. (Advisor); Igor Adamovich Prof. (Committee Member); Sandip Mazumder Prof. (Committee Member); David Hurley Dr. (Committee Member) Subjects: Condensed Matter Physics; Materials Science; Mechanical Engineering; Nanoscience; Nuclear Engineering; Nuclear Physics

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, University of Akron, 2017, Polymer Science

Geckos are intriguing creatures, adhering to ceilings, to leafs, to glass and cement, all without glue. Instead, their adhesion is dependent on surface interactions between their hierarchical adhesive structure and the contacting substrates. These interactions on the nanoscale have significant macroscale influences. Changing the conditions between substrate and the nanostructures of the gecko adhesive affects the ability of geckos to adhere. Improving our understanding of how these conditions affect the adhesion of the natural gecko system can then inform our synthetic adhesive design efforts. Here, I have investigated how geckos perform on 'soft' substrates and on rough underwater substrates. Taking inspiration from the hierarchical nanostructure of the gecko adhesive, and its interactions with water, hierarchical rough carbon nanotube substrates were used to investigate the roles of roughness and surface chemistry on superhydrophobic stability. The 3D structure of CNTs was further used to investigate the influence of surface interactions on the macroscale thermal conductivity properties.

Committee: Ali Dhinojwala Dr. (Advisor); Yu Zhu Dr. (Committee Chair); Gary Hamed Dr. (Committee Member); Mesfin Tsige Dr. (Committee Member); Peter Niewiarowski Dr. (Committee Member) Subjects: Condensation; Experiments; Nanoscience; Physics; Polymers; Zoology

Master of Science, University of Akron, 2014, Biomedical Engineering

Current commercially available prosthetic liners and sockets insulate the residual limb, causing the temperature of the residual limb to increase. As a result, the residual limb sweats excessively, leading to numerous dermatologic conditions. These skin problems can impart physical and psychological burdens on the amputee patient and hinder their rehabilitation process. Overall, this study aimed to aid in the rehabilitation of amputee patients by specifically addressing the cause of the increased residual limb temperatures. This was accomplished in three aims. The first aim focused on quantifying the thermal barrier posed by materials currently used in prosthetic liners and sockets by measuring the materials’ thermal conductivities. All materials were shown to be significant insulators. The second aim approached the problem of increased temperatures by modifying a prosthetic socket, then using computer simulations to observe the temperature difference between the inner and outer socket walls. Three sockets were modeled: two modified sockets, each containing a cooling channel 0.5 cm in diameter; and a control socket. A greater temperature drop across the socket wall suggested that the socket could provide cooling benefits to the residual limb by allowing for heat to be drawn away from the limb, towards the cooling channels. Socket type and location on the socket were statistically significant factors affecting the predicted temperature difference. This finding suggests that modifications of a prosthetic socket could offer a cooling effect to amputee patients. Aim 3 focused on validating that computer simulation from Aim 2. 3D printed prototype sockets were constructed. The socket with the greatest observed average temperature differential was the socket with an eight revolution cooling channel in its wall. This finding suggests that socket modifications, like the cooling channel presented, could provide a cooling effect to the residual limb. O (open full item for complete abstract)

Committee: Brian Davis Dr. (Advisor); Marnie Saunders Dr. (Committee Member); Narender Reddy Dr. (Committee Member) Subjects: Biomechanics; Biomedical Engineering; Biomedical Research; Engineering; Polymers

MS, University of Cincinnati, 2013, Engineering and Applied Science: Mechanical Engineering

This study simulated a 3D model of a tablet device to predict/analyze the temperature distribution inside the device. Temperatures of some specific internal components are also predicted. The tablet device chosen was an Apple iPad 2 and was studied by a teardown process to get the layout and locations of all the components of interest. Power was supplied to the tablet through wall outlet and this power was measured using wires - one end of the wires was used to tap the power lines under specific components, and the other end was supplied to a data acquisition (DAQ) software unit. The DAQ module was connected to a laptop to record power and temperature data when an application is run on the tablet. Most of the component powers were obtained from the experiments and unknown power values were calculated using Goalseek option in Excel. Three workloads - Idle, HD Video Streaming and Skype Video Calling were tested with an emphasis on the latter two workloads. 'Hotspot' locations on the front and back sides of the tablet were obtained, using an IR camera, after performing an initial run on the workloads until the workload reached steady state. Thermocouples were then placed at the Hotspot locations on the outside of the tablet to record temperature data. Thermocouples were placed on the internal components such as SoC (System on Chip) or Processor, PMIC (Power Management Integrated Circuit) and Memory of the tablet to record their temperatures. The numerical model of the tablet was generated in FloTHERM from the dimensions obtained from the teardown. Material properties were assigned to all the components. Power sources were applied to the components that generated heat to correspond to the experimental work. The grid was generated in FloTHERM and the maximum aspect ratio of the mesh was within the acceptable range specified by FloTHERM. Board Conductivity and PMIC sensitivity studies were performed on the tablet for the Skype Video Calling workload for (open full item for complete abstract)

Committee: Urmila Ghia Ph.D. (Committee Chair); Kirti Ghia Ph.D. (Committee Member); Milind Jog Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2009, Food Science and Nutrition

High pressure processing (HPP; 100-700 MPa at temperatures < 45°C) and pressure-assisted thermal processing (PATP) (500-700 MPa; 90-120°C) have been used to inactivate pathogenic and spoilage bacteria and produce high quality foods. The objectives of this dissertation were to evaluate the influence of various pressure-temperature combinations on quality, microbial lethality and thermophysical properties of selected foods. Experiments were conducted to investigate the influence of process temperature (95-121°C) at different pressures (0.1, 500-700 MPa) on carrot quality. Results indicated that under comparable process temperatures (up to 105°C), pressure-assisted thermal processing (PATP) retained the carrot quality attributes such as color and carotene content better than thermal processing (TP). However, process and preprocess thermal history greatly influenced carrot textural change. Pressure protective effects on product hardness at elevated temperatures (110-121°C) were less pronounced. Subsequently, experiments were conducted to evaluate the role of pressure during sequential (pressure pre-treatment at ambient temperature followed by TP) or simultaneous (PATP) treatment in preserving product quality attributes. To learn how different food matrices are influenced by various pressure-heat combinations, experiments were also carried out using carrot, jicama, red radish, zucchini, and apricot. Results showed that TP degraded product texture severely but HPP followed by TP improved texture retention. In comparison to TP alone, PATP better retained texture and color. The beneficial effects of PATP may come from the densification of the tissue due to pressurization or biochemical changes of the pectic substances. Texture retention was product dependent, with jicama being the least influenced among the foods tested. An instrumental based crunchiness index (CI) was developed and validated using sensory data. CI was able to describe textural transformation of various p (open full item for complete abstract)

Committee: V.M. Balasubramaniam PhD (Advisor); Sudhir Sastry PhD (Committee Member); Ahmed Yousef PhD (Committee Member); Luis Rodriguez-Saona PhD (Committee Member) Subjects: Food Science

Doctor of Philosophy, The Ohio State University, 2007, Materials Science and Engineering

The efficacy of ceramic thermal barrier coatings (TBCs) used to protect and to insulate metal components in engines increases with the thickness of the TBCs. However, the durabilities of thick TBCs deposited using conventional ceramic-coating deposition methods have not been adequate. Here the feasibility of depositing highly durable thick TBCs (1.5 to 4 mm thickness) of ZrO2-7 wt.% Y2O3 (7YSZ) on bond-coated superalloy substrates using the solution-precursor plasma spray (SPPS) method has been demonstrated. Thermal cyclic durabilities of the thick SPPS TBCs have been shown to be much superior compared to TBCs deposited using the conventional air-plasma-spray (APS) process. To evaluate the performance of thick APS and SPPS TBCs, mechanical properties of free-standing coatings and coating/substrate interfaces have been determined experimentally. Additional evaluation of TBC performance has been obtained from studies of damage and development of thermally grown oxide (TGO) at the interface as a result of thermal cycling. The later results are used to suggest mechanisms of chemical failure of TGO in thick plasma-sprayed TBCs. Based on the experimental results and numerical analysis of the TBC residual stresses, the dramatic improvement in the thermal cycling life in the SPPS TBCs is attributed to superior mechanical properties of SPPS coatings. The presence of the strain tolerant vertical cracks in SPPS TBCs reduces the driving force for TBC spallation under mode-II loading. Additionally, high in-plane fracture toughness in the SPPS TBCs under mode-I loading delays the TBC spallation significantly. Finally, thermal conductivity of the SPPS TBCs has been reduced by microstructural tailoring. Analytical and object-oriented finite element (OOF) models have been used to analyze the experimental thermal conductivity data, and to predict thermal conductivities of engineered TBCs.

Committee: Nitin Padture (Advisor); Sheikh Akbar (Other); John Morral (Other) Subjects: Engineering, Materials Science

Doctor of Philosophy (Ph.D.), University of Dayton, 2010, Engineering

The need for advanced thermal management materials is well recognized in the electronics and communication industries. An overall reduction in size of electronic components has lead to higher power dissipation and increased the necessity for innovative cooling designs. In response, material suppliers have developed and are continuing to develop, an increasing number of light weight thermal management materials. The new carbon foam is a low density and high thermal conductivity material which has the potential to radically improve heat transfer, thereby reducing size and weight of equipment while simultaneously increasing its efficiency and capabilities. However, carbon foam exhibits low strength and low heat capacity. The present work is intended to overcome these two main drawbacks using a combinatorial approach: (i) initially, copper coating was carried out to improve the thermo-mechanical properties of carbon foam. The thermal and mechanical properties of coated foam were measured using laser flash technique and compression test, respectively. An analytical model was developed to calculate the effective thermal conductivity. It was observed that the copper-coated carbon foam with 50% porosity can attain a thermal conductivity of 180 W/mK. The results from the analytical model were in a very good agreement with experimental results. The modulus increased from 4.5 MPa to 8.6 MPa and the plateau stress increased from 54 kPa to 171 kPa. The relationships between the measured properties and the copper weight ratio were determined. The above analyses demonstrated the significance of copper coating in tailoring carbon foam properties. (ii) Numerical and experimental studies were performed to analyze the phase change behavior of wax/foam composite encapsulated in metal casing. A two-energy equation model was solved using computational fluid dynamics software (CFD). Interfacial effects at the casing-composite junction and between the wax-foam surfaces and the capillary pr (open full item for complete abstract)

Committee: Khalid Lafdi (Committee Chair); Lawrance Flach (Committee Member); Kelly Kissock (Committee Member); C. William Lee (Committee Member); Youssef Raffoul (Committee Member) Subjects: Engineering

Master of Engineering, Case Western Reserve University, 2009, EMC - Mechanical Engineering

Developments in modern electronics are hindered by smaller devices creating more heat without better cooling methods. Better heat dissipating materials are sought to lower operating temperatures, and an increasing number of micro and nanostructures are being developed for such use. Testing these one dimensional structures is difficult due to their microscopic scale, so a new method is developed for measuring the thermal properties of high thermal diffusivity micro and nanofibers. This method builds upon previous techniques to remove inaccuracies and unnecessary complications. The result is the thermal flash technique used here to measure the thermal properties of a variety of carbon based structures, focusing on a fiber composed of polyimide and coal tar pitch developed at the University of Akron. An investigation into the thermal properties of these fibers as a function of pitch is presented, and the results compare within +/- 5% to reported values in the literature.

Committee: Alexis R. Abramson PhD (Advisor); Joseph M. Prahl PhD (Committee Member); Yasuhiro Kamotani PhD (Committee Member) Subjects: Engineering

Master of Science (MS), Ohio University, 2012, Mechanical Engineering (Engineering and Technology)

Highly conductive graphitic foams are currently being studied for use as thermal conductivity enhancers (TCEs) in thermal energy storage (TES) systems. TES systems store energy using the latent heat capacity of phase change materials (PCMs). Due to the low thermal conductivity of most PCMs, TCEs are necessary to evenly distribute heat throughout the PCM. Graphitic foams have been used as TCEs due to their high thermal conductivity, high specific surface area, and low weight. This thesis describes the experimental research at Ohio University to determine the thermal conductivity and transient thermal response characteristics of foams infiltrated with PCMs. Methods have been developed to modify highly conductive open celled graphitic foam by filling them with epoxy. This allowed the testing of graphitic foams using classical experimental thermal measurement methods. Thermal conductivity of foams tested ranged from 12 W/mK to 135 W/mK. It was found that graphitic foams can increase the thermal diffusivity of PCMs by a factor of 400+. This leads to thermal responses 9 times lower when graphitic foams are used as TCEs.

Committee: Khairul Alam (Advisor); Howard Dewald (Committee Member); Frank Kraft (Committee Member); Valerie Young (Committee Member) Subjects: Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2025, Macromolecular Science and Engineering

Hexagonal boron nitride is a platelet-like thermally conductive filler commonly used to increase the thermal conductivity of polymers. Good alignment of boron nitride in the in-plane direction is required to create a good network for phonon transport to achieve high thermal conductivity in composite materials. To create good alignment of platelet-like particles, extensional flow is needed, like what is experienced by a polymer melt in a layer multiplication element in forced assembly co-extrusion. As a result, films with A/B structure of hBN + polymer/unfilled polymer were made using layer multiplication co-extrusion. The high degree of alignment and confinement of boron nitride into every other layer led to a higher-than-expected thermal conductivity at relatively low loadings of boron nitride. At only 12.7vol% (25wt%) filler loading, a composite film reached a thermal conductivity of 3.41 Wm-1K-1 which is much higher than was predicted by modeling.

Committee: Gary Wnek (Advisor); Gary Wnek (Committee Chair); Lei Zhu (Committee Member); Joao Maia (Committee Member); Svetlana Morozova (Committee Member) Subjects: Materials Science; Plastics

Doctor of Philosophy, The Ohio State University, 2024, Nuclear Engineering

Actinide oxide fuels undergo complex and multifaceted transformations during reactor operation, which, if properly understood and accounted for, can significantly enhance the safety and stability of the fuel cycle. A key aspect of understanding these transformations is identifying the critical features of fuel microstructure that impact thermal conductivity. This thermal conductivity is influenced by intricate microstructural, chemical, and thermodynamical processes. Due to substantial thermal variations across the annular pellet, significant microstructural changes occur over short distances, and these processes are highly temperature-dependent. Thus, a coupled approach to simulating the multiscale features of nuclear fuels is essential for predicting the evolution of thermal systems in actinide oxides. While accurately accounting for microstructural changes in nuclear fuels has been crucial to the industry since its inception, localized thermal conductivity measurements have recently emerged as a method to validate thermal conductivity models that have been standard for decades. Novel experimental techniques, offering unprecedented levels of discretization, now capture these localized microstructural trends affecting the thermophysical properties of nuclear fuel. Previous studies on the validation and parameterization of thermal conductivity in nuclear fuels were limited by the measurement scale, often spanning millimeters using techniques such as Laser Flash Analysis. The thermal conductivity microscopes, however, provide micron-scale resolution, enabling more precise validation across the spatial dimensions of nuclear fuels. In this study, radial measurements of porosity, elemental composition, and thermal conductivity of oxide nuclear fuel pellets at various burnups were acquired and analyzed in conjunction with a fuel performance model integrated with the experimental results. The nuclear fuel performance software BISON was used to integrate the multiscale m (open full item for complete abstract)

Committee: Carol Smidts (Committee Member); Tunc Aldemir (Committee Member); Marat Khafizov (Advisor); Tsvetoslav Pavlov (Committee Member) Subjects: Nuclear Engineering