Thesis (M.S.)--University of Michigan, 1978.

Thesis (M.S.)--University of Michigan, 1978.

Thesis--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Water is a limited resource and pollution has become an increasing problem due to industrialization. Aromatic organic pollutants are resistant to biodegradation, and thus chemical methods like the Fenton reaction is required for degradation. The Fenton reaction is catalyzed by cobalt oxide. This study aims to investigate the effect of size and shape of cobalt oxide nanoparticles on the catalytic activity. Methylene blue (MB) was used as a model pollutant. The size and shape of nanoparticles are known to influence the activity of catalysts. The study used a precipitation method to prepare spherical and cubic-shaped cobalt oxide nanoparticles of different sizes using preparation parameters like cobalt precursor, amount and type of oxidant and time of reaction. The XRD patterns of all the prepared cobalt oxide nanoparticles showed a pure cubic Co3O4 phase. The shape of the nanoparticles changed from spherical to cubic when the cobalt precursor was changed from cobalt nitrate to cobalt acetate. The size of the nanoparticles increased when lower amounts of hydrogen peroxide and longer reaction times were used. Nanoparticles between 4.6 to 19.5 nm for spherical particles and between 6.6 and 43.3 nm for cubic particles were prepared. FTIR spectra analysis showed the presence of both nitrate and acetate ions on the surface of cobalt oxide nanoparticles. The TGA results indicated that the adsorption of the acetate ions is stronger than the nitrate ions on the surface of the cobalt oxide nanoparticles. The rate of degradation of methylene blue, the pseudo first order rate constant and the amount of leaching increased with a decrease in the nanoparticles size. The Turn Over Frequency (TOF), which is the moles of methylene blue converted per mole of surface cobalt atoms, decreased with a decrease in the size for both the spherical and cubic nanoparticles. The TOF for the spherical and cubic nanoparticles were similar indicating that the catalytic activity may not be dependent on the shape of the nanoparticles. FTIR analyses showed that degradation occurred, and that methylene blue was not just decolourised to leuco methylene blue.

The tricobalt cluster PhCCo3(CO)9 (1) reacts with the bidentate phosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) in the presence of added Me3NO to give the diphosphine-substituted cluster PhCCo3(CO)7(bma) (2). Cluster 2 is unstable in solution, readily losing CO to afford Co3(CO)6[(μ2-η2/η1-C(Ph)C=C(PPh2)C(O)OC(O)](μ2-PPh2) (3) as the sole observed product. VT-31P NMR measurements on cluster 2 indicate that the bma ligand functions as both a chelating and a bridging ligand. At -97 °C, 31P NMR analysis of 2 reveals a Keq of 5.7 in favor of the bridging isomer. The bridged bma cluster 2 is the only observed species above -50°C. The solid-state structure of 2 does not correspond to the major bridging isomer observed in solution but rather the minor chelating isomer. The conversion of 2 to 3 followed first-order kinetics, with the reaction rates being independent of the nature of the reaction solvent and strongly suppressed by added CO, supporting a dissociative loss of CO as the rate-determining step. The activation parameters for CO loss were determined to be ΔH≠ = 29.9 ± 2.2 kcal/mol and ΔS≠ = 21.6 ± 6 eu.

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Submitted in fulfillment of the requirements for the Degree of Master of Technology: Chemical Engineering, Durban University of Technology. Durban. South Africa, 2015. / Cobalt powder is a grey metallic powder that is produced by the thermal decomposition and reduction of a cobalt compound. The challenge faced by Shu Powders Africa was that sub-micron cobalt powder had never been produced in a two-step furnace by any manufacturer in the cobalt powder industry. Hence there was no prior information to guide this type of processing. Therefore this research set out to investigate the production of sub-micron cobalt powder through a two-step furnace to determine the optimum parameters for this process. For the company to remain competitive, it was imperative to begin producing sub-micron cobalt powder. Sub-micron cobalt powder is much more valuable and profitable to produce. The second production line would be operational due to the production of sub-micron cobalt powder hence creating job opportunities for the local community. Sub-micron cobalt powder shares the same chemical composition and physical characteristics as cobalt powder. The only differences are particle size (0.60 - 0.90 µm), oxygen content (0.30 - 0.80%) and the microscopic structure which is the particle size distribution d90 (7 - 10 µm). The approach taken was to understand the variables that had a large effect on the powder. The effects needed to be established by determining how it impacted on the quality of the powder which is pertinent to making sub-micron cobalt powder. Due to the experience in producing cobalt powder, variables that had a large effect on normal cobalt powder production were assumed to be the same variables that would impact the production of sub-micron cobalt powder. Some of these effects were also confirmed by literature. A strategy of statistical design of experiments was used to evaluate the conditions for sub-micron cobalt powder production. Design of experiments assisted in planning the experimental design matrices for both experiments. For the furnace experimentation a 24 factor design was selected. For the jet mill experimentation a 23 factor design was selected. Response surface methodology was used to determine optimum ranges of the variables at various process conditions. The central composite rotatable design laid out the design in which the variables interacted with one another at different process conditions. Evaluation of results was based on the generated model. Models such as the 3D surface model, cubic model and the contour model were generated to graphically illustrate the effects that the variables have on the response. Analysis of furnace data indicated that the optimal response was achieved at a temperature range (445 - 460)°C, hydrogen gas range (225 - 250) Nm3/h, belt speed (80 - 90) mm/min, and carbon dioxide gas range (80 - 90) Nm3/h. Analysis of the jet mill experimental data indicated that the optimal response particle size distribution, was achieved at a classifier speed range of (5500 - 6000) rpm, AFG grinding bin range (30 - 35) kgs and grinding gas pressure of (4.0 - 4.5) bar. The study confirms the efficiency of a two-step furnace to produce sub-micron cobalt powder at high volumes. The advantage of the two-step furnace was the increased throughput of 2.3-2.7 tons/day whilst in industry furnace throughputs are 1.3-1.6 tons/day. This represented a 60% increase in productivity over conventional furnaces. The response surface methodology also proved to be a suitable technique for process optimization.

published_or_final_version / Chemistry / Master / Master of Science