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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
671

Carbon nanotube and nanofiber reinforcement for improving the flexural strength and fracture toughness of portland cement paste

Tyson, Bryan Michael 2010 May 1900 (has links)
The focus of the proposed research will be on exploring the use of nanotechnology-based nano-filaments, such as carbon nanotubes (CNTs) and nanofibers (CNFs), as reinforcement in improving the mechanical properties of portland cement paste as a construction material. Due to their ultra-high strength and very high aspect ratios, CNTs and CNFs have been used as excellent reinforcements in enhancing the physical and mechanical properties of polymer, metallic, and ceramic composites. Very little attention has been devoted on exploring the use of nano-filaments in the transportation industry. Therefore, this study aims to bridge the gap between nano-filaments and transportation materials. This will be achieved by testing the integration of CNTs and CNFs in ordinary portland cement paste through state-of-the-art techniques. Different mixes in fixed proportions (e.g. water-to-cement ratio, air content, admixtures) along with varying concentrations of CNTs or CNFs will be prepared. Different techniques commonly used for other materials (like polymers) will be used in achieving uniform dispersion of nano-filaments in the cement paste matrix and strong nano-filaments/cement bonding. Small-scale specimens will be prepared for mechanical testing in order to measure the modified mechanical properties as a function of nano-filaments concentration, type, and distribution. With 0.1 percent CNFs, the ultimate strain capacity increased by 142 percent, the flexural strength increased by 79 percent, and the fracture toughness increased by 242 percent. Furthermore, a scanning electron microscope (SEM) is used to discern the difference between crack bridging and fiber pullout. Test results show that the strength, ductility, and fracture toughness can be improved with the addition of low concentrations of either CNTs or CNFs.
672

Fabrication and Functionalization of Graphene and Other Carbon Nanomaterials in Solution

Widenkvist, Erika January 2010 (has links)
In the last decades several new nanostructures of carbon have been discovered, including carbon nanotubes (CNTs), and the recently discovered 2-dimensional graphene. These new materials exhibit extraordinary and unique properties—making them extremely interesting both for fundamental science and for future applications. It is, however, of crucial importance to develop new and improved fabrication and processing methods for these carbon nanomaterials. In this thesis the concept of applying solution chemistry and solution-based techniques to fabricate and to deposit graphene and other carbon nanomaterials is explored. An area-selective deposition method was developed for CNT and carbon-coated iron nanoparticles. By utilizing organic functionalization the properties of the nanomaterials were tuned, with the purpose to make them soluble in a liquid solvent and also enable them to selectively adsorb to non-polar surfaces. The first step of the functionalization process was an acid treatment, to introduce defects in the materials. This method was also used to create defects in so-called carbon nanosheets (CNS). The effect of the defect formation on the electric properties of the graphene-like CNS was studied; it was found that the resistance of the CNS could be reduced to 1/50 by acid treating of the sample. Also, the effect of the created defects on gas adsorption to the surface of the CNS has been investigated. This was done using atomic layer deposition (ALD) of TiO2 on the CNS, and a clear change in nucleation be-havior was seen due to the acid-treatment. Furthermore, a solution-based new method for fabrication of graphene was developed; this method combines intercalation of bromine into graphite with ultrasonic treatment to exfoliate flakes into a solvent. From the solvent the flakes can be deposited onto an arbitrary substrate. Several important parameters in the method were investigated in order to optimize the process. One important parameter proved to be the choice of solvent in all steps of the procedure; it was shown to influence sonication yield, flake size, and deposition results. Toluene was identified as a suitable solvent. A mild heat-treatment of the starting material was also identified as a way to increase the exfoliation yield. Using this method, fabrication of few-layer graphene sheets was achieved and areas down to 3 layers in thickness were identified—this is in the very forefront of current solution-based graphene fabrication techniques.
673

Automated Enrichment of Single-Walled Carbon Nanotubes with Optical Studies of Enriched Samples

Canning, Griffin 13 May 2013 (has links)
The design and performance of an instrument is presented whose purpose is the extraction of samples highly enriched in one species of single-walled carbon nanotubes from density gradient ultracentrifugation. This instrument extracts high purity samples which are characterized by various optical studies. The samples are found to be enriched in just a few species of nanotubes, with the major limitation to enrichment being the separation, rather than extraction. The samples are then used in optical and microscopic studies which attempt to determine the first absorption coefficient (S1) of the (6,5) species of nanotube. Initial experiments give a value of 9.2 ± 2.6 cm2 C atom-1. Future work is proposed to improve upon the experiment in an attempt to reduce possible errors
674

Laser-initiated Coulomb explosion imaging of small molecules

Brichta, Jean-Paul Otto January 2008 (has links)
Momentum vectors of fragment ions produced by the Coulomb explosion of CO2z+ (z = 3 - 6) and CS2z+ (z = 3 - 13) in an intense laser field (~50 fs, 1 x 1015 W/cm2) are determined by the triple coincidence imaging technique. The molecular structure from symmetric and asymmetric explosion channels is reconstructed from the measured momentum vectors using a novel simplex algorithm that can be extended to study larger molecules. Physical parameters such as bend angle and bond lengths are extracted from the data and are qualitatively described using an enhanced ionization model that predicts the laser intensity required for ionization as a function of bond length using classical, over the barrier arguments. As a way of going beyond the classical model, molecular ionization is examined using a quantum-mechanical, wave function modified ADK method. The ADK model is used to calculate the ionization rates of H2, N2, and CO2 as a function of initial vibrational level of the molecules. A strong increase in the ionization rate, with vibrational level, is found for H2, while N2 and CO2 show a lesser increase. The prospects for using ionization rates as a diagnostic for vibrational level population are assessed.
675

Laser-initiated Coulomb explosion imaging of small molecules

Brichta, Jean-Paul Otto January 2008 (has links)
Momentum vectors of fragment ions produced by the Coulomb explosion of CO2z+ (z = 3 - 6) and CS2z+ (z = 3 - 13) in an intense laser field (~50 fs, 1 x 1015 W/cm2) are determined by the triple coincidence imaging technique. The molecular structure from symmetric and asymmetric explosion channels is reconstructed from the measured momentum vectors using a novel simplex algorithm that can be extended to study larger molecules. Physical parameters such as bend angle and bond lengths are extracted from the data and are qualitatively described using an enhanced ionization model that predicts the laser intensity required for ionization as a function of bond length using classical, over the barrier arguments. As a way of going beyond the classical model, molecular ionization is examined using a quantum-mechanical, wave function modified ADK method. The ADK model is used to calculate the ionization rates of H2, N2, and CO2 as a function of initial vibrational level of the molecules. A strong increase in the ionization rate, with vibrational level, is found for H2, while N2 and CO2 show a lesser increase. The prospects for using ionization rates as a diagnostic for vibrational level population are assessed.
676

Carbon Nanotube Synthesis for Microsystems Applications

Sunden, Erik Oscar 23 June 2006 (has links)
Modern day engineering systems research presently lacks techniques to exploit the unique properties of many nanomaterials; coupled with this challenge exists the need to interface these nanomaterials with microscale and macroscale platforms. A nanomaterial of particular interest is the carbon nanotube (CNT), due to its enhanced physical properties. In addition to varied electrical properties, the CNT has demonstrated high thermal conductivity and tensile strength compared to conventional fiber materials. CNTs are beginning to see commercial applications in areas in which sufficient study has been dedicated. While a large part of the worldwide focus of CNT research has been in synthesis, an equally important area of research lies in CNT integration processes. The unique and useful properties of many nanostructured materials will never be realized in mainstream manufacturing processes and commercial applications without the proper exploration of integration methods such as those detailed in this thesis. The primary motivation for the research detailed in this thesis has been to develop CNT synthesis processing techniques that allow for novel interfacing methods between carbon nanotubes and eventual applications. In this study, an investigation was performed to look at several approaches to integrating CNTs into micro-electromechanical systems (MEMS). Synthesis of CNTs was studied in two different settings. Synthesis was first performed, directly on the microsystem, via a global scale chemical vapor deposition (CVD) process. Secondly, synthesis was performed directly onto a microsystem device via localized resistive heating. Following synthesis, the application of atomically layered, protective coatings was then investigated. Integration methods were then investigated to allow for CNT transfer to microsystem applications incapable of withstanding synthesis temperatures. The developed integration methods were evaluated by creating functional microscale electrical circuits in flexible substrates via hot emboss imprint lithography. Lastly, post synthesis processing methods were used to create micropatterned cell guidance substrates as well as neuronal stimulating substrates.
677

An Assessment Study of Automotive Engine Carbon Removal Technology

Chiu, Ting-Cheng 17 July 2010 (has links)
Human large-scale use of coal, oil, natural gas and other fossil fuels, which emit large quantities of energy use is caused by the greenhouse effect of greenhouse gases, including carbon dioxide increases rapidly, is the culprit of global warming. Man type and species of global warming has brought the threat of the living environment, how to effectively slow down global warming has become the man to face critical issues. According to Taiwan's greenhouse gas emissions from all sectors data show that the transport sector with a significant contribution to greenhouse gas emissions, developed with the vehicle industry, motor vehicles have become the main transport means of transport to daily life, but also resulted in major metropolitan areas and air pollution from carbon dioxide, improve air quality and reduce carbon emissions, should have to be propaganda vehicle maintenance and regular inspection of work, vehicle maintenance facilities for the engine than coke will effectively reduce unnecessary vehicle emissions and pollution, with a view to sustainable human development. This study to collect relevant information through expert interviews, sorting out the market viability of the Automotive engine carbon removal methods are "bubble-type engine than coke," the "trickle engine program than coke" and "In addition to product hydrogen aircraft engine Carbon Programme "of three. And to identify factors that impact assessment, "the cost of implementation", "when applied to pollution assessment," "clear the effect of coke", "engine damage effects" and "ease of handling," and five. Main and analytic theory, experts in the field to conduct the carbon removal of the vehicle engine is assessed for the valid questionnaires, the use of AHP Analysis Method Comparison of the order of priority or importance, to find consistency through the whole management of the common point of view. Comprehensive management and access to the whole study found that industry, government, science and other 12 experts were assessing the overall level of the importance of the five ranking for the "impact of engine damage," the most important, were "clear the effect of coke," " when applied to pollution assessment, "" implementation costs "," easy operation "of the last. The engine in the current market feasible than carbon technology, the experts unanimously agree that the "hydrogen aircraft engine program than coke," the most advantage of the actual promotion of environmental protection that, the Government Ying Ying Zao Leung good conduct political Peihehuanjing, provide economic incentives to encourage people to Automotive engine carbon removal and counseling industry to promote environmental protection measures. The research results could serve as references for the Government's future vehicles and the carbon reduction policies.
678

Electrodeposition of Diamond-like Carbon thin films on Silicon and their Characteristical

Wu, Jian-Guang 27 July 2010 (has links)
Diamond-like carbon (DLC) film exhibits an extreme hardness, low friction coefficient, chemical stability, heat conductivity, high resistance, and high optical transparency. There properties lead to remarkable on industrial applications Diamond-like carbon films were deposited onto the silicon (100) and ITO glass substrates. Under the same deposition conditions, the characteristics of DLC films were evaluated by the variations of deposited parameters such as the applied voltage, deposition temperature the concentrations of electrolyte; acetic acid. The properties due to the different substrate were compared and discussed in detail. In experimental work, the properties of DLC film were conducted by various measurements. Scanning electron microscopy can make an insight into the surface morphology also to reveal the uniformity of the DLC films. For the I-t curves of DLC film growth, it can be used to study of the growth mechanism by correlation the surface morphology observed by Scanning electron microscopy (SEM). The transmission, refraction index and optical band gap of DLC film was measured by the N &K analyzer. Finally, the hydrogen content, composition and microstructure of DLC films were characterized by the FTIR and XPS analyze According to above results, DLC film using the electrolyte of acetic acid was more difficult to deposit on Silicon substrate because the very high activation energy and the high hydrogen ion existing in DI water firstly deposited on the surface of Si substrate. For FTIR measurement, The absorption wavenumber of various bonding observed were positioned at 610 cm-1,680 cm-1,1100 cm-1 and 3600 cm-1~3800 cm-1and to be cauterized as the bonding of Si-H¡BSi-O and O-H, respectively. The absorption peaks within the range from 2800 cm-1 to 3100 cm-1 were missing. Peaks observed were attributed to the bonding of Si-C¡B SP3 C-C¡B C-O¡BC-C¡BC=O and C=C and the CHn bonding was missing on the surface of substrate. The reaction mechanism of DLC deposition can be suggested from the results of measurements. As bias voltage applied, the acetic ion; CH3COO- were attracted by the Anode as the state of C¡]Anode¡^-OOCCH3, and then to give electron and form the CH3+ion»PCO2. The hydrogen ion and methyl ion were attracted by cathode. The competitive reaction was built between ions to deposited DLC films and/or to form Si-H. However, experimental results show that the last was preferred and for forming the DLC film was forbidden.
679

Processing and Characterization of Carbon Nanotubes Reinforced Epoxy Resin Based Multi-scale Multi-functional Composites

Thakre, Piyush R. 2009 December 1900 (has links)
This research is focused on investigating the effect of carbon nanotubes on macroscale composite laminate properties, such as, interlaminar shear strength, interlaminar fracture toughness and electrical conductivity along with studying the micro and nano-scale interactions of carbon nanotubes with epoxy matrix via thermomechanical and electrical characterization of nanocomposites. First an introduction to the typical advanced composite laminates and multifunctional nanocomposites is provided followed by a literature review and a summary of recent status on the processing and the characterization work on nanocomposites and composite laminates. Experimental approach is presented for the development of processing techniques and appropriate characterization methods for carbon nanotubes reinforced epoxy resin based multi-functional nanocomposites and carbon fiber reinforced polymer composite laminates modified with carbon nanotubes. The proposed work section is divided into three sub-sections to describe the processing and the characterization of carbon nanotube reinforced epoxy matrix nanocomposites, woven-carbon fabric epoxy matrix composite laminates modified with selective placement of nanotubes and unidirectional carbon fiber epoxy matrix composite laminates modified with carbon nanotubes. Efforts are focused on comparing the effects of functionalized and unfunctionalized carbon nanotubes on the advanced composite laminates. Covalently functionalized carbon nanotubes are used for improved dispersion and fiber-matrix bonding characteristics and compared with unfunctionalized or pristine carbon nanotubes. The processing of woven carbon fabric reinforced epoxy matrix composite laminates is performed using a vacuum assisted resin transfer molding process with selective placement of carbon nanotubes using a spraying method. The uni-directional carbon fiber epoxy matrix pre-preg composites are processed using a hot press technique along with the spraying method for placement of nanotubes. These macroscale laminates are tested using short beam shear and double cantilever beam experiments for investigating the effect of nanotubes on the interlaminar shear stress and the interlaminar fracture toughness. Fractography is performed using optical microscopy and scanning electron microscopy to investigate the structure-property relationship. The micro and nano-scale interactions of carbon nanotubes and epoxy matrix are studied through the processing of unfunctionalized and functionalized single wall carbon nanotube reinforced epoxy matrix nanocomposites. The multifunctional nature of such nanocomposites is investigated through thermo-mechanical and electrical characterizations.
680

Temporal and Spatial Variability of Organic Carbon Isotopic Compositions of Particles Collected from Sediment Traps in the Western Okinawa Trough

Chuang, Tzu-Shen 14 July 2000 (has links)
Abstract This study is to investigate the spatial and temporal variabilities of geochemical and carbon isotopic compositions of particles collected in the region off northeast Taiwan. Organic carbon isotopic compositions (d13Corg), total organic carbon content (TOC) and C/N ratio were determined in sediment particles collected at different water depths from three time-series sediment traps (at T12, T13, and T18 stations, respectively). The results showed abnormally high mass fluxes than those previously found. Generally they increase with water depths, implying both the transport from Lanyang-Hsi River and the resuspension from the seafloor. TOC contents range from 0.5 to 1.5wt% and decrease with depths. This can be attributed to changes in the surface productivity, lateral transport and organic preservation. The organic carbon isotopic compositions range between -21 and -25o/oo, which falls well within the d13Corg values of continental margin sediments. The lower d13Corg values at T12 station than those at T13 station can be attributed to the large terrestrial inputs. It is noted that d13Corg values decrease with depths, suggesting a significant contribution of the horizontal transport of particles to the settling process.

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