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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.
31

An Investigation Into Activated Carbon

Kyriakakis, G 02 July 2015 (has links)
The extraction of aurocyanide by activated carbon probably involves the adsorption of neutral ion-pair species [M ^jAuCCN)^. The large hydrophobic aurocyanide anion associates with the cation in order to minimize the disruption of the water structure whereby lowering its free energy
32

The impact of structure on the electrical transport properties of nitrogen-doped carbon microspheres

Marsicano, Vincent Derek January 2016 (has links)
A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. April 2016. / Chemical vapour deposition was used to synthesise four carbon microspheres (CMS) samples. Introduction of acetonitrile in different quantities produced spheres of differing nitrogen concentration. The structure of the spheres was investigated using Raman spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy techniques. The Raman investigation revealed a decrease in average graphitic flake size which forms the surface layers of the spheres with nitrogen incorporation. XPS showed that increased nitrogen doping caused a larger proportion of pyridinic nitrogen, which process likely restricts the growth of the crystallite flakes detected with the Raman technique. Microscopy revealed spheres with differing morphologies which did not correlated with the level of nitrogen doping. Electron paramagnetic resonance techniques were employed to investigate the impact of nitrogen doping on the spin system of the samples. Electrical transport and Hall effect data were collected with an automated experiment station purpose built for this work. Samples displayed semiconducting behaviour at low temperatures which was ascribed to fluctuation assisted tunnelling. At higher temperatures all four samples display a transition to metallic behaviour. Models for conduction, which were tested but ultimately rejected, include variable range hopping in all its dimensional forms, Efros-Shklovskii VRH and weak localisation. A comparison of the conduction results and the structural information showed the conductivity to be more closely affected by the structure of the spheres than the overall doping level. A case is made for the dominant conduction mechanism being determined by the intersphere rather than the intrasphere conduction. This research shows that creating carbon microspheres with specific electrical properties requires control of the structure induced during synthesis. Nitrogen doping alone does not determine the final physical and electrical transport properties. / LG2017
33

The solubility of carbon dioxide in waters of low alkalinity

Jones, Mark Murrison 06 1900 (has links)
A graphical method, based on a set of acid-base titrations, is presented for the determination of the carbon dioxide speciation in natural solutions. The application of this method, in conjunction with measurements of the partial pressure of carbon dioxide with which our solutions were in equilibrium permitted the calculation of the solubility of carbon dioxide. The results of these calculations in dilute solutions of 1.00 meq/l alkalinity gave a value of 0.070 for the solubility at 25° C. This value is considerably higher than that obtained by Harned and Davis (1943), 0.0345, for solutions of zero alkalinity. Our experimental method, with the conditions used by Harned and Davis, yielded a result which agreed well with theirs. It is concluded that the solubility of carbon dioxide within the alkalinity range found in many fresh waters, is greater than was previously believed. The reason for this higher solubility is not known. It is shown that it cannot be ascribed to a specific cation effect. / Graduation date: 1969
34

Development and evaluation of a thermal/optical method for the analysis of carbonaceous aerosol /

Johnson, Richard Lee. January 1981 (has links)
Thesis (M.S.) - - Oregon Graduate Center, 1981.
35

Study on the CVD growth and analyses of Carbon Nanotube

Chu, Chun-Chi 28 January 2004 (has links)
In this work, carbon nanotubes (CNTs) have been synthesized by microwave chemical vapor deposition technique using Ni as catalyst and at different experimental parameters. Catalysts Ni plays an important role in the process of synthesizing carbon nanotubes. Sputtered Ni film can agglomerate into uniformly distributed nanometer size particles, which can be employed to assist the growth of carbon nanotubes. The effect of Ni catalyst on CNTs growth have been investigated and an optima Ni thickness has been found. There are series experiments performed in order to improve the CNT growth environment and a characteristics for CNTs under the condition at 30 torr, 800¢J, 600W and ¡V 350V was observed. The growth characteristics was evaluated with TEM, SEM, Raman and FTIR. From Raman spectra, the degree of graphitization is proportional to growth temperature and microwave power. In addition to extending the growth time, the length of CNT did not increase.
36

Grassland carbon and nitrogen dynamics: effects of seasonal fire and clipping in a mixed-grass prairie of the southern great plains

Harris, Wylie Neal 16 August 2006 (has links)
Plant production and soil microbial biomass (SMB) in grassland ecosystems are linked by flows of carbon (C) and nitrogen (N) between the two groups of organisms. In native mixed grasslands of the southern Great Plains, these cycles are strongly influenced by climate. They may also be modulated by the timing and intensity of disturbances such as fire and clipping. We assessed the relative influence of climate and disturbance on plant community and soil C and N dynamics. Combined effects of fire and clipping were assessed in a 2x3 factorial design including spring fire and light clipping or continuous clipping. Seasonal fire effects were evaluated in a one-way analysis incorporating spring and fall fire in unclipped plots. Plant cover and biomass (by functional type), litter mass, SMB C and N, soil density fraction concentration and composition, soil organic C, total N, and inorganic N, soil temperature and moisture, soil respiration, and net N mineralization were measured at monthly intervals. C4 grasses were unaffected by fire or clipping, probably as a result of summer drought in both studyyears. Clipping reduced cover of C3 annual grasses but increased that of C3 perennials, resulting in no net change in C3 grass biomass. Fire did not affect C3 grass cover or biomass. Both fire and clipping reduced litter mass. This was reflected in seasonal declines in SMB C in fire treatments, suggesting that the primary input of microbial C in this ecosystem occurs by decomposition of current-season plant litter. Litter removal offers a single mechanism by which fire-induced increases in soil temperature and reductions in light soil density fraction concentration, soil moisture, and net N mineralization rates may be explained. Lack of treatment effects on soil respiration rates suggest that plant roots represent an important component of the plant-soil C cycle, not quantified in this research. Overall, treatment effects were relatively minor compared to seasonal climate-related changes in response variables, particularly in light of repeated summer drought.
37

The effects of carbon nanotube reinforcement on adhesive joints for naval applications

Burkholder, Garrett L. January 2009 (has links) (PDF)
Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Kwon, Young W. Second Reader: Pollak, Randal D. "December 2009." Description based on title screen as viewed on January 29, 2010. Author(s) subject terms: Carbon nanotubes, CNTs, MWNTs, nanocomposites, carbon fiber composite, adhesive strength, crack propagation, Mode II, functionalized carbon nanotubes, carboxyl. Includes bibliographical references (p. 38-40). Also available in print.
38

The optical characterization of 0.4 nm single-walled carbon nanotubes /

Cheng, Kit Yee. January 2003 (has links)
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 91-92). Also available in electronic version. Access restricted to campus users.
39

Properties of small radius single-wall carbon nanotubes from first-principles calculations /

Liu, Huijun. January 2003 (has links)
Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.
40

Evaluation of dynamic properties of a carbon - carbon composite at elevated temperatures /

Bunker, Shaun Patrick, January 2002 (has links)
Thesis (M.S.) in Mechanical Engineering--University of Maine, 2002. / Includes vita. Includes bibliographical references (leaves 96-97).

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