Browsing by Author "Wren, E"

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    Characterisation of phase relations and properties in air-oxidised Ti3SiC2
    (Elsevier, 2007-09-25) Low, IM; Wren, E; Prince, KE; Atanacio, AJ
    The oxidation of Ti3SiC2 in air from 25 to 1450 degrees C is characterised by differential thermal and gravimetric analysis (DTA/TGA), X-ray diffraction (XRD), grazing-incidence synchrotron radiation diffraction (GISRD), neutron diffraction (ND), transmission electron microscopy (TEM), secondary ions mass spectroscopy (SIMS) and Vickers indentation. The diffraction results show that rutile formed at a temperature of similar to 750 degrees C. A glassy phase - formed at > 1000 degrees C - devitrified upon cooling to room temperature to form tridymite but crystallised to cristobalite at temperatures >= 1300 degrees C. Composition depth-profiling of the surface layer oxides by XRD, GISRD and SIMS revealed a graded distribution of phases (TiO2, SiO2 and Ti3SiC2) both at the nanoscale (<= 1100 degrees C) and microscale level (1200 degrees C), which is particularly distinct at the interfaces. The oxide layers also exhibit a graded variation in microhardness. © 2007, Elsevier Ltd.
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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.