3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Resin-gel synthesis and characterisation of copper and titanium mixed metal oxides nanoparticles(2014-08-21) Dziike, FaraiThe resin-gel method of synthesis successfully produced compounds of mixed metal oxides of copper titanium oxide powders of the form CuxTiyOZ with different compositions. These include Cu3TiO5, Cu3TiO4, Ti3Cu3O, Cu2Ti4O, Cu2Ti2O5 and Cu2TiO3. Heat-treatment of the powders at 300°C, 500°C, 700°C and 900°C for 1 hour was performed to determine the full composition/temperature phase diagram. The target particle size was in the 10- nanometer range, and for most of the samples, this size was achieved. Powder xray diffraction and transmission electron microscopy were the main techniques used to study the crystallization of these materials and their transformation to other polymorphic phases under different temperatures. Phase-match, particle size analysis and TEM imaging determined the properties and characteristics of the respective crystallographic phases of these materials. TEM analysis showed that some powders agglomerated while others exhibited both regular and irregular morphologies and polydisperse particle size distribution. Only a single unique phase was identified, but its structure could not be determined.Item Thermoresponsive behaviour of selected mixed metal oxides(2014-02-25) Nyoni, Michelle SibonokuhleLow-to-negative thermal expansion is an important property for materials in a wide range of applications including space applications, microwave components, construction, mirrors, dental fillings and high precision ion dilatometers. Powder X-ray diffraction (PXRD) has been used to investigate the thermoresponsive behavior of Nb6.7W10.3O47, Ta14.8W1.2O46, Ta16W18O94 and BaPbO3. Calibration and benchmarking of the diffractometer was performed to ensure accurate results are obtained. Continuous Online X-ray Analysis (COXA) enabled the close monitoring of phase transitions, changes in any lattice parameters in response to thermal stimuli. When COXA is coupled with Rietveld refinement, coefficients of thermal expansion (CTE) could be determined accurately. The tungstates were synthesized using a precipitation reaction and heat treatment from chlorides of the metals (NbCl5; TaCl5) and tungstic acid (H2WO4). The products, Nb6.7W10.3O47, Ta14.8W1.2O46 and Ta16W18O94, underwent a COXA analysis within the temperature range 30 ˚C to 900 ˚C. Nb6.7W10.3O47 has a mean volumetric CTE of 6.704 x 10-6 ˚C-1, and therefore has low positive thermal expansion. The tantalum tungstates were found to have low positive thermal expansion as well. Ta14.8W1.2O46 and Ta16W18O94 have mean volumetric CTEs of 2.101 x 10-5 ˚C-1 and 9.851 x 10-6 ˚C-1. BaPbO3 underwent two phase transitions between 30 ˚C and 550 ˚C from orthorhombic Imma to I4/mcm to cubic Pm-3m. The transition from Imma to I4/mcm took place at 270 ˚C. The phase transition from I4/mcm to Pm-3m took place at 390 ˚C.