Browsing by Author "Oo, Z"

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    Depth-profiling of surface composition in air-oxidised Ti{sub 3}SiC{sub 2}
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2005-11-20) Low, IM; Wren, E; Oo, Z; Prince, KE; Atanacio, AJ
    Titanium silicon carbide (Ti3SiC2) is a remarkable ternary compound that defies many of the expected properties of a ceramic. It has better thermal and electrical conductivity than titanium metal, is resistant to thermal shock, and is relatively light. Its hardness is exceptionally low for a carbide, and like graphite, it is readily machinable. Hitherto, mixed and confusing results have been reported for the oxidation resistance and behaviour of Ti3SiC2 in air. For instance, the oxidation resistance of Ti3SiC2 was reported to be excellent at temperatures below 1100 degrees C due to the formation of a protective SiO2 surface layer. However, oxidation of Ti3SiC2 was detected to commence as low as 400 degrees C through the formation of an anatase-like TiO2 film that eventually transformed to rutile at 1050 degrees C. In addition, although the existence of the protective TiO2 (rutile) has been confirmed by all the researchers, the presence of the protective SiO2 film is much more elusive. In a recent study, the oxidized layers were reported to exhibit a duplex microstructure in the temperature range 1000-1500 degrees C with an outer layer of TiO2 (rutile) and an inner layer consisting of SiO2 and TiO2. In a similar study, researchers also found the protective oxide scales that formed to be layered with the inner layer composed of silica (∼1200 degrees C) and titania and the outer layer comprised of pure rutile (∼900 degrees C). The growth of these oxide layers is both temperature and time-dependent and was thought to occur by the outward diffusion of titanium and carbon and the inward diffusion of oxygen through surface pores or cracks. However, the nature and precise composition of the oxide layers formed during oxidation remain controversial, especially in relation to the presence of SiO2 and the graded nature of the oxides formed. In this paper, the surface composition depth-profiles of air-oxidized Ti3SiC2 have been investigated by secondary ion mass spectroscopy (SIMS) in the temperature range 500-1400 degrees C. Line scan and near-surface depth profiling by SIMS have revealed a distinct gradation in phase composition within the surface oxide layers.
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    Effect of vacuum annealing on the phase stability of Ti3SiC2
    (Wiley-Blackwell, 2007-08) Low, IM; Oo, Z; Prince, KE
    The effect of vacuum annealing on the thermal stability and phase transition of Ti3SiC2 has been investigated by X-ray diffraction (XRD), neutron diffraction, synchrotron radiation diffraction, and secondary ion mass spectroscopy (SIMS). In the presence of vacuum or a controlled atmosphere of low oxygen partial pressure, Ti3SiC2 undergoes a surface dissociation to form nonstoichiometric TiC and/or Ti5Si3Cx that commences at ~1200°C and becomes very pronounced at ≥ 1500°C. Composition depth profiling at the near surface of vacuum-annealed Ti3SiC2 by XRD and SIMS revealed a distinct gradation in the phase distribution of TiC and Ti5Si3Cx with depth. © 2007, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
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    Mapping of composition, phase transitions and properties in oxidized Ti3SiC2
    (Scientific.Net, 2008-02-01) Oo, Z; Low, IM; Palmquist, JP; Avdeev, M
    The oxidation characteristics, composition profile and phase transition of Ti3SiC2 in the temperature range 20-1400°C have been investigated by in-situ neutron diffraction and secondary ion mass spectroscopy (SIMS). Anatase has been observed to form at ~600°C, rutile at ~750°C and cristobalite at ∼1300°C. Depth-profiling results by SIMS and Vickers indentation have revealed a distinct gradient in composition and microhardness within the surface oxide layers. © 2021 by Trans Tech Publications Ltd.