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School of Materials Science and Engineering

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https://hdl.handle.net/1853/70762

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College of Engineering

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Publication Search Results

Now showing 1 - 10 of 16

Optimizing Pressure in Compressive Textiles and Utilizing Smart Sensors to Monitor Patient Recovery

(Georgia Institute of Technology, 2019-05) Vagott, Jacob N.

This study was designed to examine how to better monitor patients throughout compression therapy. Compressive wraps are used to optimize blood flow in patients in order to encourage proper healing and decrease the likelihood of medical complications. The pressure being applied by the wrap determines its effectiveness, so it would be ideal if this could be monitored real-time. New advancements in smart sensors may allow for this to occur. Until then, it would be useful to have tables of elongation versus pressure, so that doctors and nurses have a reference that can be used to estimate the pressure being applied to the wound. Temperature and moisture sensing were also considered, since they could be used to monitor patient temperature and potentially sense fluid build-up. Skin temperature sensing was found to be possible using the SensorPush Temperature and Humidity Sensor. A table has been fabricated using tensile test data that shows the acceptable range of percent elongations for each tested compressive wrap. It was determined that stress relaxation is prevalent in compressive wraps, and this must be taken into consideration in future testing.
Load Dependent Fatigue Crack Initiation in High Purity Al

(Georgia Institute of Technology, 2018-05) Wang, Xueqiao

Fatigue crack initiation sites and mechanisms in metals and alloys have long been investigated, since metal components are often subjected to cyclic loading, and fatigue cracking is one of the major causes of failure. Therefore, understanding the dominant cracking mechanism under different conditions is essential for tailoring the composition and microstructure of metal components for better fatigue resistance under various loading conditions. Load dependent fatigue response in high purity aluminum (Al) is investigated. In low cycle fatigue, extrusions and intrusions are found to form on grain boundaries (GBs), especially prevalently at triples junctions. However, contrary to theories on extrusion formation from persistent slip bands (PSBs), no slip bands are observed in these specimens. Dislocation cells, on the other hand, are observed to form in higher densities and smaller sizes as stress amplitude increases. As extrusion formation occurs only after a threshold number of cycles, it might be a result of the progression of dislocation cell formation. In high cycle fatigue, no extrusions are observed at GBs, while microcracks form within grains. Therefore, high cycle fatigue life may be controlled by mechanisms other than dislocation cell formation, and involves transgranular, rather than intergranular, fracture.
Atomic Layer Deposition of Sub-Nanometer Inorganic Layers on Natural Cotton to Enhance Oil Sorption Performance in Marine Environments

(Georgia Institute of Technology, 2018-05) Short, Andrew E

Over 1 million tons of oil is inadvertently spilled each year. The economic and environmental costs of these spills are enormous and necessitate further development of environmentally friendly sorbent materials. Here, we demonstrate a vapor phase modification approach to create a new class of oil sorbents composed of cellulosic materials (cotton) coated with a sub-nanometer layer of inorganic oxide. This new cellulosic sorbent remains buoyant in water indefinitely and achieves a selective oil sorption capacity (23 g g-1 or 1.05 g cm-3) that is at least 35x better than untreated cellulose in aqueous environments. This new sorbent particularly excels under “realistic” conditions like continuous agitation (e.g. simulated waves) and pre-soaking in water (e.g., rain or forced immersion). When sorption performance is compared on a per-volume basis—which better captures use conditions than a per-mass basis—this modified natural product becomes comparable to the best sorbents reported in the literature, most of which require further expensive processing.
Applicability of Cytocompatible ALD Barrier Films as Protective Barriers for Biological Implants

(Georgia Institute of Technology, 2018-05) Adstedt, Katarina

The ability of atomic layer deposited (ALD) metal oxide films to serve as protective, encapsulating barriers for biological implants is determined through testing the corrosion resistance and degradation behavior of the films. Using plasma enhanced ALD (PE-ALD), metal-oxides are deposited at 100 oC onto gold electrodes. Through MTT cell proliferation assay, the films are determined to be cytologically compatible and will not cause harm to the implant host. Using electrochemical impedance spectroscopy (EIS), the films establish their relative chemical stabilities within three different biological environments, phosphate buffer solution (PBS), simulated sweat and simulated saliva. The resulting data from the EIS measurements demonstrates the rate of degradation for the four respective films and exhibits which films are best suited as protective barriers for biological implants. ALD Al2O3 is not suitable as an encapsulating layer as it demonstrates no corrosion resistance. Within PBS, ALD TiO2 establishes itself as the most stable film barrier while within simulated sweat and saliva ALD ZrO2 is the most chemically stable. The viability of ALD films in biological solutions and their enhanced corrosion resistances opens up the possibility for a new class of materials that can be used for the protection of bioimplants and wearable devices.
The Effects of Polycrystalline Silicon Photovoltaic Cells on Unmanned Aerial Vehicle Performance

(Georgia Institute of Technology, 2017-05) Pyronneau, Ponthus

The objective of this study was to investigate the differences in performance between monocrystalline silicon and monocrystalline silicon photovoltaic cells in addition to the effects on the performance of solar powered unmanned aerial vehicles. This was accomplished by casting both monocrystalline and polycrystalline silicon solar cells optimized for the specific test drone of the study and then observing the differences in electrical and mechanical performance. Performance parameters that were examined in depth included endurance, range, power to weight ratio, lift to weight ratio as well as power differences between both types of photovoltaic cells. In addition, examination of how much absorption of solar radiation occurred within the actual cells, and observation of any other optical phenomenon were performed. The cells were further characterized by examining the correlation between the solar cell microstructure and observed performance. The results of this study will potentially benefit the fields of materials science, aerospace, and electrical engineering by confirming that a cheaper means of fabricating solar cells will yield relatively higher performance data.
The structural coloration mechanisms of Morpho butterfly wing scales

(Georgia Institute of Technology, 2016-07-18) Liu, Chunzi

Many bright colors in nature are generated by the optical effects of biological structures. These intricate structures, combined with the absorption and reflection effects of the chemical pigments within, provide the observed color with high visibility and some other startling optical properties. A prominent example comes from the iridescent colors observed on the wing scales of Morpho, a family of subtropical butterflies. Iridescent color refers to the color which changes with varying viewing angle. It is proposed that a layered structure alternating in refractive indices produces the observed colors on the butterfly wing scales, but this generalized idea does not explain some optical effects observed through a variety of methods. This research suggests that the structures in the lower lamina also contributes to the macroscopic optical effects. The observation methods used in this research include optical microscopy, spectroscopy, integrating sphere analysis, and scatterometry. The scatterometry visualizes the far field optical effects from all viewing angles simultaneously. Elementary explanations are proposed for the unexpected patterns observed in the experiments.
Low-Cost Hydrothermal Synthesis of Porous Carbon Spheres with Tunable Particle Size

(Georgia Institute of Technology, 2016-05) Hong, Junghwa

Spherical porous carbon particles find applications in gas storage, biological and medical sorbents, energy storage devices and other demanding applications. At the same time, the common routes for their synthesis are elaborate and costly. Here we report on our study of a low-cost synthesis of spherical carbons with uniform and tunable diameter. The application of a lowtemperature hydrothermal process greatly accelerates the rate of cross-linking within polymer precursors, allowing formation of individual spherical carbon particles upon subsequent polymer carbonization. By reducing the precursor concentration we have demonstrated particle size reduction from 1,250 to 140 nm. The as-produced particles exhibit disordered microstructure with very smooth particle surface and open internal micro-porosity.
Stretchable and transparent silicone/zinc oxide nanocomposite for advanced LED packaging

(Georgia Institute of Technology, 2014-04-30) Zhao, Xueying

At present, one of the key challenges in the light-emitting diode (LED) packaging technology is light extraction due to the difference in index of refraction between LED chip and air. Silicone nanocomposites have been extensively researched for applications in LED encapsulant to reduce such difference in refractive index. It is well-known that silicone is desirable for LED encapsulant because of its optical transparency and photothermal resistance. However, not much has been accomplished to leverage the elastic properties of silicone for enabling a stretchable LED encapsulant. In this work, I aim to investigate the stretch ability of silicone/zinc oxide (ZnO) nanocomposites for LED packaging. Wurtzite ZnO nanoparticles were prepared in colloids and subjected to silane treatment. Effects of both ex situ and in situ silane treatment on the final mechanical and optical properties of the silicone/ZnO nanocomposites were examined. Silicone/ZnO nanocomposites exhibit significantly more compliant stress-strain behavior than silicone control. In particular, silicone/silane-treated ZnO nanocomposites show more serrated stress-strain curves. They also embrace higher transmittance than silicone/unmodified ZnO nanocomposites, indicating an improvement in the dispersion of the nanoparticles. It was found that the silicone/5% silane-treated ZnO nanocomposite prepared by an in situ method was able to deform over a range of up to 160%. The film made of this unique silicone/ZnO nanocomposite (~40 microns thick) exhibits transmittance >70% throughout the visible range.
Thin Films Made From Colloidal Antimony Tin Oxide Nanoparticles for Transparent Conductive Applications

(Georgia Institute of Technology, 2013-05-08) Halim, Abigail

In this study, antimony tin oxide (ATO) nanoparticles from Alfa Aesar were redispersed in water using tetramethylammonium hydroxide (TMAH) as a dispersing agent and deposited onto glass substrates by spin coating. Films of one to five layers were made. These thin films were characterized using impedance spectroscopy and ultraviolet-visible spectroscopy to obtain their resistances and optical transmittance, respectively. The films displayed sheet resistances around 10⁵-10⁴ kΩ/􏰀 and optical transmittance in the near infrared to near ultraviolet range above 95%. Films were then made using a higher concentration ATO solution and found to achieve sheet resistances on the order of 10 ² kΩ/􏰀. Impedance measurements, along with optical micrographs, were taken at different locations on the films, demonstrating that films of more than one layer showed greater uniformity. Further sets of films were also produced with varying substrate preparation and dispersion deposition parameters. Aside from dispersion concentration, high humidity during film measurement was found to be the most crucial parameter for achieving low sheet resistances.
Effects of microstructure on the susceptibility of austenitic and martensitic stainless steels to pitting and intergranular corrosion in aqueous chloride environments

(Georgia Institute of Technology, 2012-05-07) Sikri, Tarun Vabhav Pratap

Stainless steels are utilized for their high toughness and resistance to general corrosion. Austenitic (300 series) stainless steels are the most popular because they are ductile and can be easily formed into desired geometries. They can also be case hardened to form alternating layers of martensitic and austenitic microstructures for applications that require high toughness and resistance to surface wear. However their usage is limited in comparison to other ferrous alloys due to higher initial costs and susceptibility to pitting and intergranular (IGC) corrosion. A microcell was developed to study these localized corrosion phenomena in microstructural regions of interest by performing polarization (spot) tests within well defined areas on metallic surfaces. Spot tests across profiles of welded 304 stainless steel confirmed that sensitization, greater acidities and higher chloride contents increase susceptibility and greater additions of chromium and nickel reduce susceptibility to localized corrosion. Spot tests across a case hardened (CSS 42L) stainless steel profile revealed that the austenitic sensitized outer layer was more susceptible to localized attack compared to the martensitic matrix. A more complete understanding of how microstructure affects these localized corrosion processes will lead to better alloy modifications, service environments and maintenance making this class of material a more sustainable alternative.