Browsing by Author "Topic, Mira"

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    An investigation of phase transformations in Pt-V coating systems
    (2012) Makhetha, William Motsoko; Lang, Candy; Topic, Mira
    Phase transformations in Pt-V coatings after heat treatment have been investigated. Five Pt- V ordered phases (PtV, PtV 3 , Pt 2 V, Pt 3 V and Pt 8 V) have been previously observed in bulk platinum-vanadium alloys. Phase formation in coatings is expected to be sequential and controlled by the lowest temperature eutectic (liquidus) composition; this allows control of experimental parameters for formation of desired ordered phases. This investigation included fabrication of coatings, heat treatments, morphology characterization and phase analysis. Single and multilayer coatings ranging between 0.07 μm and 0.5 μm were deposited on vanadium and platinum substrates using E-beam deposition. The kinetics of phase transformation were studied by subjecting the coated layers to a variety of heat treatments in the temperature range 600°C to 900°C for 4 and 8 hours. Composition and morphology characterization was carried out using EDS and SEM respectively. XRD was used for phase analysis. Four (PtV, PtV 3 , Pt 2 V, Pt 3 V) out of the five Pt-V ordered phases exhibited in bulk alloys, were successfully formed from the coating system investigated in this project. The first phase formed, and the sequence of phase formation, was found to be different depending on which metal formed the substrate. The vanadium-rich ordered phase (PtV 3 ) was preferentially formed first on vanadium substrates and the sequence of phase formation progressed through ordered phases richer in platinum. The platinum-rich ordered phase (Pt 3 V) was preferentially formed first on platinum substrates and the sequence continued towards formation of ordered phases richer in vanadium. An increase in heat treatment temperature from 600°C to 900°C resulted in rapid kinetics of phase transformation but affected the morphology of the coatings. An increase in coating thickness, number of coating layers, heat treatment time, and temperature resulted in an increase in overall total number of ordered phases and volume of ordered phases.
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    Structural and electrical characteristics of printed metal nanoparticle networks
    (2016) Van den Berg, Claire Barbara; Blumenthal, Mark; Topic, Mira; Härting, Margit
    The structural and electrical properties of metal nanoparticle (NP) networks and their dependence on the constituent phases have been investigated. Percolation and effective media theories have been used to describe the physical properties of disordered systems, as well as providing a link between their structural features and the corresponding electrical transport properties. Silver and palladium nanoparticulate layers in ethyl cellulose polymer binder (ETHOCELTM), were fabricated onto paper using the method of screen printing. The metal-binder ratios were varied in order to observe changes in the microstructure when a percolating network consisting of the metal NPs is formed through the layer.
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    The synthesis of novel Pt-based nanoparticles
    (2011) Leteba, Gerard; Lang, Candace; Topic, Mira
    The ultimate goal of this project was to explore alternative and various synthetic routes for the design and fabrication of V@Pt core-shell and bimetallic nanoparticles.