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This dissertation details research aimed at the separation of Zr and Hf in the tetrafluoride form. Separation of ZrF4 and HfF4 was achieved using sublimation followed by desublimation. The separation involves the sublimation of the tetrafluorides in an inert atmosphere under controlled parameters. The sublimed mass (700 C to 800 C) diffuses into nitrogen which then flows across a water-cooled desublimer (annulus) with the aim of desubliming the one metal fluoride in preference to the other. This implies that separation was achieved in both the sublimer and the desublimer, due to differences in both the sublimation and desublimation rates. The aim was for the sublimer residue to be Hf-rich and the desublimer content to be Zr-rich. The Zr/Hf content was determined by means of ICP-OES analysis. It must be noted that the work reported in this thesis is based on only a first sublimation step. The reason for this is that the equipment used was on laboratory scale and that the mass collected from the desublimer was not sufficient to allow a second or third step to be carried out. Little information was available in the literature on the sublimation separation of Zr and Hf, especially in the fluoride form, most of it being sublimation under vacuum conditions. On an industrial scale, only vacuum sublimation of ZrF4 has been introduced into the industry, and no information was found for sublimation of ZrF4 in an inert atmosphere on an industrial scale. There was also limited information on the sublimation rate of ZrF4 or HfF4 in an inert atmosphere. In the process described in this dissertation, optimal temperature selection is crucial since low temperatures result in a low sublimation rate, and high temperatures not only increase the level of impurities in the sublimed product, but also increase the cost of construction material and energy consumption. The aim was to determine the experimental conditions, i.e. sublimation time, temperature and position on the desublimer, which will provide optimal separation conditions. These conditions must, however, be compared with the operating cost, as this will be higher at a higher temperature and for longer sublimation runs. / Dissertation (MEng)--University of Pretoria, 2018. / Chemical Engineering / MEng / Unrestricted

Organophosphonates have been used as simulants of highly toxic compounds such as chemical warfare agents in the study of the decomposition reactions that occur on the surface of hafnium dioxide. Metal oxide and metal-oxide nanoparticles have been shown to decompose organophosphonate molecules. In this study, high surface area hafnium oxide nanoparticles are synthesized via laser ablation. This creates nanoparticles that are free of contaminants and have a narrow size distribution. The particles are characterized by atomic force microscopy and scanning electron microscopy to determine particle size and thin film morphology. Once characterized, they are exposed to dimethyl methylphosphonate and the surface reaction is analyzed by reflection-absorption infrared spectroscopy. / Master of Science

The chemistry of hafnium oxide based and materials are described in the context of ion exchange and lithography. HafSOx, represented by the composition HfO₂₋[subscript x](SO₄)x, is described to possess a significant capacity towards ion exchange in acidic and basic solutions, enabling films of HafSOx to be cleanly and readily be converted to oxide films by neutralization. The optical properties, composition and morphology of these oxide films are characterized. The fabrication of mixed metal oxide films is demonstrated via solution and ion exchange routes. This thesis also explores the photoresist chemistry of HafSOx resists. A photoreaction mechanism based on the decomposition of peroxide is proposed. In addition, the patterning of HafSOx films by 193 nm, extreme ultraviolet (EUV) and electron beam radiation is described, and the influence of composition on its photoresist properties is studied. / Graduation date: 2012

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Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Jack C. Lee. Vita. Includes bibliographical references. Also available from UMI.