Thesis (M. Sc.)(Metallurgical Engineering)--University of Pretoria, 2003. / Summaries in Afrikaans and English. Includes bibliographical references. Available on the Internet via the World Wide Web.

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Liquid Phase Deposited (LPD) TiO2 film technology and the characterization of films were described in detail in this thesis. The LPD-TiO2 film can be utilized in electrochromic, photocatalyst and gas sensor devices. The optimum parameters for deposition of LPD-TiO2 were studied. First of all, we study the deposition properties and deposition parameter of LPD-TiO2 film. The effect of heating treatment on LPD-TiO2 film was investigated in this thesis. The as-deposited LPD-TiO2 film is amorphous and the TiO2 anatase phase can be obtained by annealing at 400 ¢J. The rutile phase can be observed at the annealing temperature of 900 ¢J. After annealing, the crystalling characteristic of LPD-TiO2 film can be improved and its refractive index can reach 2.46 annealed in O2 ambience. Its dielectric constant can be as high as 17 at annealing temperature of 700 ¢J in O2 ambience. LPD-TiO2 film can deposit on GaAs substrate successfully. The GaAs was etched by the treatment solution during deposition. Therefore, Ga and As are contained in the LPD film. The C-V characterization can be improved at annealing 400 ¢J. But the leakage current increases with higher annealing temperature. The electrochromic (EC) phenomena of TiO2 have been first reported by Inoue et al., where the films are prepared by hydrolysis of titanium tetraoxide. The film shows cathodic coloration and turns dark blue. The LPD-TiO2 film was deposited at 40 ¢J with (NH4)2TiF6 in the process of 0.1 M and 0.2 M boric acid. The films were transparent in the visible range and can be colored in a 1M LiClO4 + propylene carbonate solution. The deposition rate can be controlled quite well at 43 nm/hours. The 270 nm thickness LPD-TiO2 film gives the best electrochromic characteristic. In order to further strength the feasibility and enlarge the application of LPD-TiO2 film. The characterizations of Nb, Au and Pt doped LPD-TiO2 film were investigated. The concentrations of Nb and Au in the film can be controlled by adjusting the concentrations of Nb and Au source solution added into the treatment solution, respectively. The Nb, Au and Pt species in the LPD-TiO2 film are Nb2O5, metallic Au and Pt(OH)x, respectively. The crystallite size of metal-doped LPD-TiO2 film is smaller than that of pure LPD-TiO2 film. The photocalytic activities of undoped and Nb-doped LPD-TiO2 film were investigated. The photocatalytic activity of Nb-doped LPD-TiO2 film is about four times higher than that of pure LPD-TiO2 film. The gas sensing properties of undoped and Nb, Au and Pt-doped LPD-TiO2 films were investigated for oxygen detection sensitivity. Experimental results show that the Nb-doped LPD-TiO2 film displays the highest in oxygen detection, and the Nb-doped LPD-TiO2 film has also a shorter response time.

Includes bibliographical references (p. 149-179).

Highway air pollution is a significant environmental threat that has staggering implications for human health worldwide. Photocatalytic materials have the potential to reduce air pollution levels near major highways using ultraviolet radiation. This project, funded by the Texas Department of Transportation, evaluated photocatalytic efficiency and durability of several commercially-available photocatalytic coatings for use on concrete structures near highways. The research presented in this thesis involved obtaining concrete highway barriers and creating concrete slabs for outdoor testing and laboratory chamber testing. Three commercially-available coatings were applied to the specimens for testing: Keim Soldalit ME paint, TxActive Stucco Cement, and Pureti Clean. Field sites were set up near major highways in Houston and Austin, Texas. Durability and photocatalytic efficiency were regularly monitored at the field sites using ion chromatography and spectrophotometry. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted on samples from each of the specimens taken before and after placement at the field sites in order to understand durability of the photocatalytic materials that were exposed outdoors. SEM results from this research project revealed that the photocatalytic material in the TxActive stucco and Keim paint remained in their original distribution after the exposure period, while the photocatalytic material in the Pureti Clean product appeared to decrease. XRD results remained fundamentally consistent for all coatings. Ion chromatography results showed that TxActive specimens had the highest surface levels of nitrates and nitrites between rainfall events, which indicates photocatalytic activity. Spectrophotometry results revealed a decrease in brightness for the Keim paint-coated specimens and no change or an increase in brightness for the TxActive stucco over time. The spectrophotometry results indicate how many surface contaminants are accumulating on the surface of a specimen, and thereby how efficiently sunlight is reaching the surface and activating the photocatalytic process. Results obtained from this research project may be influential in the selection of a means for reducing highway pollution in Texas. / text

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Silica is a common silicon dioxide (SiO2) that can be crystalline or non-crystalline (amorphous). Amorphous silica is considered to be less hazardous than crystalline silica. Three dominant crystalline polymorphs exist, with silica quartz being the most common. Exposure to respirable crystalline silica (quartz) causes silicosis, a lung scarring disease. The aim of this study was to identify and quantify the silica exposure in respirable dust personal exposure samples, as well as in representative bulk samples which are large samples taken from the sources of airborne dust obtained from different mining and production plants involved in the production of titanium dioxide from beach sand. This is needed to determine the degree of risk of developing silicosis. Forty five workers employed in different mining and production plants participated in this study. Their eight-hour personal exposure to respirable particulate was determined. Personal respirable dust exposure samples and bulk samples were analyzed for silica by an accredited laboratory by means of X-ray diffraction based on NIOSH method 7500. Silica quartz was detected in personal respirable dust samples and bulk dust samples obtained from the mining and production plants, but amorphous silica was only detected in three personal exposure samples at the Slag plant and in the bulk sample obtained from the Roaster plant. All the silica quartz and amorphous silica concentrations in personal exposure samples were well below their respective exposure limits of 0.1 mg/m3 (quartz) and 3 mg/m3 (amorphous). No significant differences were found between the silica quartz concentrations in personal respirable exposure samples obtained from the mining ponds and the production plants, although a practical significance was found between some mining and production area personal exposure samples. The non-significant differences found between exposure concentrations and a practical significance suggest the necessity of involving a larger sample group in future. Other studies done in non-mining industries showed that some workers were over exposed to respirable silica dust. Compared to these findings the results of the present study showed the opposite, with respirable silica dust levels being below the South African action level and OEL. Further research, involving more samples, spread over a longer period of time, would probably be able to show a clear trend as to how quartz structures and exposure profiles change from the mining to the various production processes. Overexposure to silica quartz anywhere at the mine and production processes is considered unlikely, with the risk of developing silicosis being low. / Thesis (MSc (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2013

Silica is a common silicon dioxide (SiO2) that can be crystalline or non-crystalline (amorphous). Amorphous silica is considered to be less hazardous than crystalline silica. Three dominant crystalline polymorphs exist, with silica quartz being the most common. Exposure to respirable crystalline silica (quartz) causes silicosis, a lung scarring disease. The aim of this study was to identify and quantify the silica exposure in respirable dust personal exposure samples, as well as in representative bulk samples which are large samples taken from the sources of airborne dust obtained from different mining and production plants involved in the production of titanium dioxide from beach sand. This is needed to determine the degree of risk of developing silicosis. Forty five workers employed in different mining and production plants participated in this study. Their eight-hour personal exposure to respirable particulate was determined. Personal respirable dust exposure samples and bulk samples were analyzed for silica by an accredited laboratory by means of X-ray diffraction based on NIOSH method 7500. Silica quartz was detected in personal respirable dust samples and bulk dust samples obtained from the mining and production plants, but amorphous silica was only detected in three personal exposure samples at the Slag plant and in the bulk sample obtained from the Roaster plant. All the silica quartz and amorphous silica concentrations in personal exposure samples were well below their respective exposure limits of 0.1 mg/m3 (quartz) and 3 mg/m3 (amorphous). No significant differences were found between the silica quartz concentrations in personal respirable exposure samples obtained from the mining ponds and the production plants, although a practical significance was found between some mining and production area personal exposure samples. The non-significant differences found between exposure concentrations and a practical significance suggest the necessity of involving a larger sample group in future. Other studies done in non-mining industries showed that some workers were over exposed to respirable silica dust. Compared to these findings the results of the present study showed the opposite, with respirable silica dust levels being below the South African action level and OEL. Further research, involving more samples, spread over a longer period of time, would probably be able to show a clear trend as to how quartz structures and exposure profiles change from the mining to the various production processes. Overexposure to silica quartz anywhere at the mine and production processes is considered unlikely, with the risk of developing silicosis being low. / Thesis (MSc (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2013