A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Characterization of Copper Covetic Bulk and Films: Copper with High Carbon Content(2016) Isaacs, Romaine Antonio; Salamanca-Riba, Lourdes G; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Incorporation of carbon nanostructures in metals is desirable to combine the strongly bonded electrons in the metal and the free electrons in carbon nanostructures that give rise to high ampacity and high conductivity, respectively. Carbon in copper has the potential to impact industries such as: building construction, power generation and transmission, and microelectronics. This thesis focuses on the structure and properties of bulk and thin films of a new material, Cu covetic, that contains carbon in concentrations up to 16 at.%. X-ray photoelectron spectroscopy (XPS) shows C 1s peak with both sp2 and sp3 bonded C measuring up to 3.5 wt.% (16 at.%). High resolution transmission electron microscopy and electron diffraction of bulk covetic samples show a modulated structure of ≈ 1.6 nm along several crystallographic directions in regions that have high C content suggesting that the carbon incorporates into the copper lattice forming a network. Electron energy loss spectra (EELS) from covetics reveal that the level of graphitization from the source material, activated carbon, is maintained in the covetic structure. Bulk Cu covetics have a slight increase in the lattice constant, as well as <111> texturing, or possibly a different structure, compared to pure Cu. Density functional theory calculations predict bonding between C and Cu at the edges and defects of graphene sheets. The electrical resistivity of bulk covetics first increases and then decreases with increasing C content. Cu covetic films were deposited using e-beam and pulsed laser deposition (PLD) at different temperatures. No copper oxide or any allotropes of carbon are present in the films. The e-beam films show enhanced electrical and optical properties when compared to pure Cu films of the same thickness even though no carbon was detected by XPS or EELS. They also have slightly higher ampacity than Cu metal films. EELS analysis of the C-K-edge in the PLD films indicate that graphitic carbon is transferred from the bulk into the films with uniform carbon distribution. PLD films exhibit flatter and higher transmittance curves and sheet resistance two orders of magnitude lower than e-beam films leading to a high figure of merit as transparent conductors.Item Mechanical and electrical properties of metal-carbon connections for battery applications(2014) Bilger, Christopher John; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Material selection and processing techniques were investigated to form carbon-metal bonds. Mechanical and electrical characterization was performed to more fully comprehend the bonding mechanisms and properties. Utilizing carbon fibers as a primary conduction medium, the specimens from the processes investigated were utilized with lithium-ion cells to further characterize the electrical performance. Electroplating nickel onto the ends of the carbon fibers provides a relatively simple processing technique which improves fiber adhesion to nickel tabs by over 4.7 times when compared to conductive silver epoxy and over 5 times greater than a 1 inch immersion of carbon fiber into a SAC305 solder ingot. Additionally, a reduction of electrical resistance by 0.7 times over the solder ingot is achieved with the electroplating technique. The results of the electroplating are achieved by using about 25% less available contact area than the solder ingot and are scalable for usage in electrical circuits.Item A TOOL FOR QUANTIFYING THE CARBON FOOTPRINT OF CONSTRUCTION PROJECTS IN THE TRANSPORTATION SECTOR(2010) Melanta, Suvish; Hooks, Elise M; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The U.S. construction industry ranks third in the nation in its production of carbon dioxide emissions. Increasing global pressure towards developing emissions reduction strategies is bound to affect the construction industry. The objective of this thesis was to develop a tool to estimate the carbon footprint of construction projects associated with transportation infrastructure. The tool determines emissions from an inventory of equipment, construction processes, and credits efforts to reduce emissions, while incorporating recent and future greenhouse gas (GHG) policies on quantifying emissions. This tool will enable construction companies to identify sources and reduce emissions, while also allowing state agencies to monitor these companies in accordance with GHG laws. The tool was applied to data associated with the construction of the Intercounty Connector, a new roadway that will connect counties in Maryland. Application of the tool to this case study showed its utility and highlighted the need for reduction strategies.Item Processing-Structure-Microstructure-Property Relationships in Polymer Nanocomposites(2008-01-31) Kota, Arun Kumar; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The optimal development of polymer nanocomposites using carbon nanotube (CNTs) and carbon nanofiber (CNFs) fillers requires a complete understanding of processing-structure-property relationships. The purpose of this understanding is to determine the optimal approach for processing polymer nanocomposites with engineered microstructures and enhanced material properties. In this research, two processing techniques were investigated: solvent processing and twin screw extrusion. The former is a batch process which employs mixing a polymer solution with a filler suspension using long mixing times and low levels of shear mixing. The latter is a continuous process that mixes polymer melts with solid nanoscale ingredients using high levels of shear mixing for a short mixing time. Previous studies conducted on polymer-CNT/CNF using these processes have focused mainly on processing-microstructure and structure-property relationships using one technique or the other. This research focuses on understanding the processing-property relationships by comparing the structure-property relationships resulting from the two processes. Furthermore, the effect of ingredients and processing parameters within each process on microstructure and structure-property relationships was investigated. The microstructural features, namely, distribution of agglomerates, dispersion, alignment, and aspect ratio of the filler were studied using optical, scanning electron, confocal and transmission electron microscopy, respectively. The composition of the filler was determined using thermogravimetric analysis. The electrical, rheological, thermo-oxidative and mechanical properties of the composites were also investigated. Many significant insights related to processing-structure-property relationships were obtained including: (a) deagglomeration is a critical combination of the magnitude of shear rate and the residence time, (b) the structure-property relationships can be modeled using a new methodology based on the degree of percolation by representing the material as an interpenetrating phase composite, (c) annealing can re-establish interconnectivity and improve electrical properties, (d) the degree of dispersion can be resolved using thermogravimetric analysis, and (e) increasing extrusion speed inhibits thermal decomposition and begins to asymptotically increase strength and stiffness through reduction in aspect ratio and size of agglomerates. Finally, a new combinatorial approach was developed for rapidly determining processing-structure relationships of polymer nanocomposites. This dissertation has broad implications in the processing of high performance and multifunctional polymer nanocomposites, combinatorial materials science, and histopathology.