[No abstract available] / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

The rate of oxidation of 99.99% and 99.999% pure copper samples at 1220°C by low-momentum jets of pure oxygen has been studied at gas flow rates of from 500 to 2000 cm³ min⁻¹. Oxidation rates at a given gas flow rate were found to be constant and were governed by starvation mass transfer kinetics. Factors studied for the reaction include: effect of lance height, effect of small additions of silicon and sulphur to the melt prior to oxidation, and effect of oxide patch area. Interfacial tension-generated flow, radially outward from the point of jet impingement, was observed during oxidation and surface velocity studies showed that such flow had a mean value of 26.1 ± 5.5 cm sec⁻¹ for all of the experiments and was independent of oxygen gas flow rate and copper bath oxygen concentration. Surface-blockage studies indicated that the bulk of the oxygen transfer to the copper occurred over the area described by the oxide patch. Liquid-phase oxygen mass transfer coefficients were calculated using the oxidation rates and oxide patch areas, and a mean value was found to be 0.104 ± 0.012 cm sec⁻¹ independent of oxygen flow rate, bath oxygen content, and dissolved sulphur and silicon contents. The rate of oxidation of 99.995% pure silver at 1100°C was studied using low-momentum jets of pure oxygen at flow rates of 1500 and 2000 cm³ min⁻¹ and was found not to be governed by starvation mass transfer kinetics. The oxidation rate was not dependent on oxygen gas flow rate and was found to be a factor of about 50 times less than those observed for copper. No spontaneous interfacial tension-generated flow was observed during oxidation of the molten silver and a possible explanation was postulated. Liquid-phase oxygen mass transfer coefficients were found to have a mean value of 2.88 ± .41 (10⁻³) cm sec⁻¹, independent of gas flow rate and bath oxygen content. The effect of interfacial turbulence on liquid-phase oxygen mass transfer coefficients in molten copper was to enhance the value by about 40 times over that observed in molten silver, where interfacial turbulence does not occur on oxidation. Copper deoxidation at 1220°C using low-momentum jets of pure hydrogen at flow rates of 1500 and 3000 cm³ min⁻¹ was studied, and was found not to depend on hydrogen flow rate, lance height, and starting oxygen concentration. The rate-controlling step was found to be the gas-phase mass transfer of hydrogen to the liquid surface for the first 3000 sec. of deoxidation. After this, liquid-phase oxygen mass transport control predominated. Dissolved silicon was found to retard the deoxidation rate, while dissolved sulphur was found to enhance the deoxidation rate through continued SO2 elimination. Interfacial tension-generated flow was observed during deoxidation and approximate surface velocities of 10 to 15 cm sec⁻¹ towards the point of jet impingement were observed. A mechanism for this flow was postulated. The gas-phase mass transfer coefficient was found to be 1.28 ± 0.25 cm sec⁻¹ for copper-oxygen alloys, and was 0.89 cm sec⁻¹ in the 1.28 ± 0.25 cm sec⁻¹ for copper-oxygen alloys, and was 0.89 cm sec⁻¹ in the presence of dissolved silicon and 2.68 cm sec⁻¹ in the presence of dissolved sulphur. An approximate value for the liquid-phase oxygen mass transfer coefficient in the liquid-phase control region was found to be 4.9 (10⁻³) cm sec⁻¹, and was found to be influenced by the presence of bubbling during this phase of deoxidation. The rate of deoxidation of molten silver at 1100°C by low-momentum hydrogen jets was studied at hydrogen flow rates of 1500 and 2000 cm³ min⁻¹ The rate was found not to depend upon hydrogen flow rate, but was found to decrease with decreasing starting bath oxygen concentration. Interfacial tension-generated flow was observed, during silver deoxidation, with approximate surface velocities of 10 to 15 cm sec⁻¹ towards the point of jet impingement. The rate-controlling step was found to be liquid-phase mass transfer of oxygen, and liquid-phase oxygen mass transfer coefficients were found to decrease with decreasing initial oxygen content. These values were enhanced by the presence of bubbling during deoxidation. Interfacial turbulence during the dissolution of solid CU₂S CU₂O, Se, and Te in molten copper was shown to occur. Values calculated for the spreading coefficient S, indicated that the spreading of these materials on molten copper was predictable. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The dehydration of isopropanol over anodic oxides was studied. The catalytic activity of the anodic oxides prepared in phosphoric, sulfuric, and oxalic acid was compared to the activity of ν-Al₂O₃. The effect of various thermal treatments on the catalytic activity was examined. IR spectroscopy proved useful for the study of the effect of thermal treatment on the acidity of the oxides. X-ray photoelectron spectroscopy (XPS) was employed to examine the oxide surfaces both before and after use as a catalyst. The acidity of the oxides was studied by various methods and related to the activity of the oxides. The acidity of the oxide surfaces was studied by the adsorption of pH indicators on the oxide surfaces. The adsorption of gaseous bases, ammonia and pyridine, was studied by IR spectroscopy and temperature programmed desorption mass spectrometry. It was thus possible to differentiate between Lewis and Brønsted acid sites and to determine the quantity of the acid sites on the various oxides. / Ph. D.

No description available.

This project was focused on the generation of porous and nanotubular anodic films on titanium and Ti-6wt.%Al alloy, and investigation of the key factors responsible for a transition between porous and nanotubular morphologies. Advanced analytical techniques were employed for characterisation of the anodic films, in particular scanning and transmission electron microscopies, including analytical transmission electron microscopy, Raman spectroscopy, nuclear reaction analysis, Rutherford backscattering spectroscopy and atomic force microscopy. Preparation of electron transparent sections for analysis by analytical transmission electron microscopy was undertaken using the focused ion beam technique. Initially, the influence of a post-anodizing rinsing treatment, using various media, on the morphology, structure and composition of anodic films generated on titanium in 0.2 M ammonium fluoride in glycerol, containing 0 and 5 vol.% added water, was investigated. Porous anodic films were formed in an electrolyte without added water followed by rinsing with ethanol. It was revealed that the oxide-rich nanotubes are embedded in a fluoride-rich matrix, with fluoride-rich material being more extensive and oxide-rich nanotubes being thinner-walled for the anodic films generated in the electrolyte with no added water followed by rinsing with ethanol compared with those for the films formed with added water to the electrolyte and rinsed similarly. However, post-anodizing rinsing of the former films transforms the porous morphology of the films to a tubular one. The contents of titanium and fluorine were reduced in the case of anodic films with the nanotubular morphology. It was suggested that dissolution of the fluoride-rich matrix occurs during rinsing of the specimens with water, leading to the transition from porous to nanotubular morphologies and subsequent loss of titanium and fluorine. Further work was undertaken to study the effect of ageing in deionised water on the morphology, structure and composition of the anodic films. It was revealed that loss of titanium and fluorine is greater for the films generated in the electrolyte with no added water followed by rinsing with water and ethanol and ageing compared with that for the films formed in the electrolyte with 5 vol.% added water followed by rinsing with water and ethanol and ageing. Finally, the anodic films generated on the Ti-6wt.%Al alloy were investigated. Porous anodic films were formed in the electrolyte without added water followed by rinsing with ethanol whereas the films treated with water disclosed nanotubular morphology. Porous anodic films contained greater amount of fluorine than nanotubular ones. Compositional analysis revealed an increased amount of fluorine for the anodic films generated on the alloy compared with those for the films formed on titanium under all investigated conditions. The difference in film compositions may be related to the difference in composition of the substrates used for anodizing, in particular, to the presence of aluminium as alloying element in the Ti-6wt.%Al alloy.

No description available.

The AAO membrane with nanopore arrays were fabricated by anodizing highly pure aluminum foils (99.9995%) in electrolyte. Ordered array have been obtained under optimized anodizing condition, and pore diameter can be controlled by different anodic voltage and electrolyte. After we got such an ordered arrangement porous alumina array, the following analysis of the material optical properties were characterized. Photoluminescence measurements showed a strong PL peak in blue. The PL peak was 420nm excited by He-Cd laser. From the transmittance spectra, the results showed that material was transparent above 400nm. The XRD spectra of AAO without and with annealing, both showed the diffraction peaks of (311)¡B(400)¡B(440), corresponding to the £^-Al2O3 phase appear. High ordered anodic porous alumina with holes interval 65nm was prepared in mixture solution of H3PO4 and H2SO4 under high temperature and high concentration. Through the use of porous anodic alumina masks, nanopore arrays were fabricated on Si¡BGaAs substrates by reactive ion etching. Also, metal nanodot arrays were formed through the AAO mask by evaporation. Thin AAO slabs also enhance the light extraction from the QDs, and control the PL emission wavelength.

No description available.

In this thesis, the growth and fabrication of the self-assembly ordered porous alumina have been investigated. First, well-ordered honeycomb array can be obtained in large area under well-anodizing condition. The diameter of formed porous alumina was about 40 to 80 nm. Pore diameter can be tuned by different voltage and electrolyte. After we got such an ordered-arrangement porous alumina array, the following analysis of the material optical properties were characterized. In the luminescence behavior, photoluminescence (PL) measurements showed a strong PL peak in blue. The PL peak was at 420 nm excited by He-Cd laser. Material transmittance was also detected, the result showed that material was transparent above 400 nm. On the other hand, the porous alumina membrane can be used as a mask. For working as negative mask, we evaporated the metal such as Au or Ti into the membrane and the metal filled into the porous to adhere to the semiconductor substrate. After lifting-off the membrane, the metal nanadots was formed on the substrate. The size and the position of these metal nanodots were distinctly-controlled by the mask. For working as replica mask, we have used the membrane as an etching mask to transfer the pattern to the semiconductor substrate successfully. This technique has the advantages of low cost and large area for nano-fabrication.