3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Use of chlorinated carbon materials to make nitrogen doped and un-doped carbon nanomaterials and their use in water treatment(2018) Maboya, Winny KgaboCarbon nanomaterials (CNMs) and nitrogen doped CNMs (NCNMs) with different morphologies were obtained by decomposition of various chlorinated organic solvents using a chemical vapor deposition (CVD) bubbling and injection methods over a Fe-Co/CaCO3 catalyst. CNFs, CNTs with secondary CNT or CNF growth, bamboo-compartmented and hollow CNTs were obtained. Increasing the growth time to 90 min resulted in growth of ~ 90 % of secondary CNFs on the surface of the main CNTs, using dichlorobenzene (DCB) as source of chlorine. The secondary CNFs grew at defects sites of the CNT wall. Secondary CNFs were not observed at other studied temperatures, 600, 650. 750 and 800 °C. Using an injection CVD method, horn-, straw- and pencil-shaped closed and open-ended CNTs/CNFs were obtained from CH3CN/DCB solutions of various volume ratios. CNT growth was enhanced after addition of chlorine. Highly graphitic carbon materials were produced from feed solutions containing low and high DCB concentrations. CNTs with defects were obtained from solutions containing 66.7 vol.% DCB. Post-doping of the N-CNTs with chlorine and of the chlorinated CNTs with nitrogen resulted in production of highly graphitic materials. Using a bubbling CVD method, mixtures of CNMs namely, hollow and bamboo-compartmented CNTs with and without intratubular junctions and carbon nano-onions filled with metal nanoparticles were obtained from feed solutions containing TTCE. MWCNT/PVP composite nanofibers were successfully synthesized using an electrospinning technique. Adsorption capacities of 15–20 g/g were obtained in pure oil or in oil-water mixtures. The adsorption capability of the MWCNT/PVP composite depended on the type of oil and its viscosity.Item The impact of structure on the electrical transport properties of nitrogen-doped carbon microspheres(2016) Marsicano, Vincent DerekChemical 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.Item The Effect of Manganese, Nitrogen and Molybdenum on the Corrosion Resistance of a Low Nickel (<2 wt%) Austenitic Stainless Steel(2007-02-22T11:27:56Z) Muwila, AsimenyeThis dissertation is a study of the effect of manganese, nitrogen and molybdenum on the corrosion behaviour of a low nickel, austenitic stainless steel. The trademarked steel, HerculesTM, has a composition of 10 wt% Mn, 0.05 wt% C, 2 wt% Ni, 0.25 wt% N and 16.5 wt% Cr. Eighteen alloys with a HerculesTM base composition were made with varying manganese, molybdenum and nitrogen contents, to establish the effect of these elements on the corrosion behaviour of the steel, and to determine a composition that would ensure increased corrosion resistance in very corrosive applications. The manganese was varied in three levels (5, 10 and 15 wt%), the molybdenum in three levels (0.5, 1 and 2 wt%) while the nitrogen was varied only in two levels (0.15 and 0.3 wt%). The dissertation details the manufacturing and electrochemical corrosion testing of these alloys. Preliminary tests were done on 50g buttons, and full-scale tests on 5 kg ingots. The buttons had a composition that was not on target, this was however rectified in the making of the ingots. Potentiodynamic tests were done in a 5 wt% sulphuric acid solution and the corrosion rate (mm/y) was determined directly from the scans. From the corrosion test results, it was clear that an increase in manganese decreases the corrosion rate, since the 5 wt% Mn alloys had the highest corrosion rate, whereas the 15 wt% Mn alloys, the lowest. The addition of molybdenum at 5 wt% Mn decreased the corrosion rate such that a trend of decreasing corrosion rate with increasing molybdenum was observed. At 10 and 15 wt% Mn molybdenum again decreased the corrosion rate significantly, but the corrosion rate value remained more or less constant irrespective of the increasing molybdenum content. At nitrogen levels lower than those of HerculesTM (less than 0.25 wt%) there was no change in corrosion rate as nitrogen was increased to levels closer to 0.25 wt%. For nitrogen levels higher than 0.25 wt%, corrosion rates decreased as nitrogen levels were increased further from 0.25 wt% but only at Mo contents lower than 1.5 wt%. The HerculesTM composition was developed for its mechanical properties. Microstructural analyses revealed that the 5 wt% Mn alloys were not fully austenitic and since the 15 wt% Mn alloys behave similarly to the 10 wt% Mn alloys, it was concluded that 10 wt% Mn was optimum for HerculesTM. All the alloys tested had a much lower corrosion rate than HerculesTM. Any addition of molybdenum thus improved the corrosion rate of this alloy. An alloy with a HerculesTM base composition, 10 wt% Mn, 0.15 wt% N and a minimum addition of 0.5 wt% Mo would be a more corrosion resistant version of HerculesTM. Pitting tests were done on the 10 wt% Mn ingots in a 3.56 wt% sodium chloride solution. The results showed that an increase in molybdenum increased the pitting resistance of the ingots. Immersion tests in a 5 wt% sulphuric acid solution at room temeperature on the 10 wt% Mn ingots confirmed that the ingots corroded by means of general corrosion.