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Effect Of Ultrasonic Treatment On The Microstructure And Mechanical Properties Of Al6061 And Composite, Ana S. Exime

FIU Electronic Theses and Dissertations

In this study, the effect of ultrasonic treatment (UST) parameters such as amplitude, sonication time, and melt temperature on microstructure and microhardness of Al 6061 alloy is evaluated. The effect of UST on the dispersion of tungsten disulfide (WS₂) and carbon nanotubes (CNT) as reinforcement particles in Al 6061 during casting is also studied. The cast Al 6061 with UST demonstrated 32% grain size reduction and 8% increase in the microhardness for optimum processing conditions. The cavitation process induced by UST is responsible for the refinement in microstructure and increase of hardness by enhancing the degassing and nucleation …

Thermodynamic Investigation Of Yttria-Stabilized Zirconia (Ysz) System, Mohammad Asadikiya

FIU Electronic Theses and Dissertations

The yttria-stabilized zirconia (YSZ) system has been extensively studied because of its critical applications, like solid oxide fuel cells (SOFCs), oxygen sensors, and jet engines. However, there are still important questions that need to be answered and significant thermodynamic information that needs to be provided for this system. There is no predictive tool for the ionic conductivity of the cubic-YSZ (c-YSZ), as an electrolyte in SOFCs. In addition, no quantitative diagram is available regarding the oxygen ion mobility in c-YSZ, which is highly effective on its ionic conductivity. Moreover, there is no applicable phase stability diagram for the nano-YSZ, which …

Hybrid Polymer Electrolyte For Lithium-Oxygen Battery Application, Amir Chamaani

FIU Electronic Theses and Dissertations

The transition from fossil fuels to renewable resources has created more demand for energy storage devices. Lithium-oxygen (Li-O₂) batteries have attracted much attention due to their high theoretical energy densities. They, however, are still in their infancy and several fundamental challenges remain to be addressed. Advanced analytical techniques have revealed that all components of a Li-O₂ battery undergo undesirable degradation during discharge/charge cycling, contributing to reduced cyclability. Despite many attempts to minimize the anode and cathode degradation, the electrolyte remains as the leading cause for rapid capacity fading and poor cyclability in Li-O₂ batteries. In this …

Electronic And Magnetic Properties Of Two-Dimensional Nanomaterials Beyond Graphene And Their Gas Sensing Applications: Silicene, Germanene, And Boron Carbide, Sadegh Mehdi Aghaei

FIU Electronic Theses and Dissertations

The popularity of graphene owing to its unique properties has triggered huge interest in other two-dimensional (2D) nanomaterials. Among them, silicene shows considerable promise for electronic devices due to the expected compatibility with silicon electronics. However, the high-end potential application of silicene in electronic devices is limited owing to the lack of an energy band gap. Hence, the principal objective of this research is to tune the electronic and magnetic properties of silicene related nanomaterials through first-principles models.

I first explored the impact of edge functionalization and doping on the stabilities, electronic, and magnetic properties of silicene nanoribbons (SiNRs) and …

Thermally-Assisted Acoustofluidic Separation For Bioanalytical Applications, Ata Dolatmoradi

FIU Electronic Theses and Dissertations

Changes in the biomechanical properties of cells accompanying the development of various pathological conditions have been increasingly reported as biomarkers for various diseases and as a predictor of disease progression stages. For instance, cancer cells have been found to be less stiff compared to their healthy counterparts due to the proteomic and lipidomic dysregulations conferred by the underlying pathology. The separation and selective recovery of cells or extracellular vesicles secreted from such cells that have undergone these changes have been suggested to be of diagnostic and prognostic value.

This dissertation first describes the implementation of a stiffness-based separation of phosphatidylcholine-based …

Development Of Novel, Microscale Fracture Toughness Testing For Adhesives, Dillon S. Watring

FIU Electronic Theses and Dissertations

The purpose of this thesis was to develop microscale fracture toughness tests to be performed in situ based off previously used macroscale fracture toughness tests. The thesis also was to use these tests to perform in situ analysis and imaging of reinforced adhesives during crack propagation. Two different fracture toughness tests were developed for this thesis through developing fixtures and sample geometry. A microscale double cantilever beam (DCB) test was developed for mode I fracture (opening mode). A microscale end notch flexure (ENF) test was developed for mode II fracture (sliding mode).

Three different types of materials were used as …

Nano-Confined Metal Oxide In Carbon Nanotube Composite Electrodes For Lithium Ion Batteries, Alexandra J. Henriques

FIU Electronic Theses and Dissertations

Lithium ion batteries (LIB) are one of the most commercially significant secondary batteries, but in order to continue improving the devices that rely on this form of energy storage, it is necessary to optimize their components. One common problem with anode materials that hinders their performance is volumetric expansion during cycling. One of the methods studied to resolve this issue is the confinement of metal oxides with the interest of improving the longevity of their performance with cycling. Confinement of metal oxide nanoparticles within carbon nanotubes has shown to improve the performance of these anode materials versus unconfined metal oxides. …

Three-Dimensional Graphene Foam Reinforced Epoxy Composites, Leslie Embrey

FIU Electronic Theses and Dissertations

Three-dimensional graphene foam (3D GrF) is an interconnected, porous structure of graphene sheets with excellent mechanical, electrical and thermal properties, making it a candidate reinforcement for polymer matrices. GrF’s 3D structure eliminates nanoparticle agglomeration and provides seamless pathways for electron travel. The objective of this work is to fabricate low density GrF reinforced epoxy composites with superior mechanical and electrical properties and study the underlying deformation mechanisms. Dip coating and mold casting fabrication methods are employed in order to tailor the microstructure and properties. The composite’s microstructure revealed good interfacial interaction. By adding mere 0.63 wt.% GrF, flexural strength was …

Deposition Of Copper Nanoparticles On 2d Graphene Nanoplatelets Via Cementation Process, Luiza Da Fontoura

FIU Electronic Theses and Dissertations

The main goal of this thesis is to deposit metal particles on the surface of 2D nanoplatelets using a controlled cementation process. As a proof of concept, copper (Cu) and Graphene Nanoplatelets (GNP) were chosen as the representative metal and 2D nanoplatelets, respectively. Specific goals of this study include depositing nanometer scale Cu particles on the surface of GNP at a low concentration (approximately 5 vol.%) while maintaining clustering and impurities at a minimum. Parametric studies were done to attain these goals by investigating various metallic reducer types and morphologies, GNP surface activation process, acid volume % and copper (II) …