Browsing by Author "Low, IM"

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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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    Comparison of thermal stability in MAX 211 and 312 phases
    (Insitute of Physics, 2010-05-03) Pang, WK; Low, IM; O'Connor, BH; Studer, AJ; Peterson, VK; Sun, ZM; Palmquist, JP
    The susceptibility of four MAX phases (Ti 2 AlC, Cr 2 AlC, Ti 3 AlC 2 , and Ti 3 SiC 2 ) to high-temperature thermal dissociation in vacuum has been investigated using in-situ neutron diffraction. In high vacuum, these phases decomposed above 1400°C through the sublimation of M and A elements, forming a surface coating of MC. The apparent activation energies for the decomposition of sintered Ti 3 SiC 2 , Ti 3 AlC 2 , and Ti 2 AlC were determined to be 179.3, -71.9, and 85.7 kJ mol −1 , respectively. The spontaneous release of Ti 2 AlC and TiC from de-intercalation during decomposition of Ti 3 AlC 2 resulted in a negative activation energy.© 2010, Insitute of Physics
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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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    Diffraction study on the thermal stability of Ti3SiC2/TiC/TiSi2 composites in vacuum
    (American Institute of Physics, 2009-06-29) Pang, WK; Low, IM; O’Connor, BH; Studer, AJ; Peterson, VK; Palmquist, JP
    Titanium silicon carbide (Ti3SiC2) possesses a unique combination of properties of both metals and ceramics, for it is thermally shock resistant, thermally and electrically conductive, damage tolerant, lightweight, highly oxidation resistant, elastically stiff, and mechanically machinable. In this paper, the effect of high vacuum annealing on the phase stability and phase transitions of Ti3SiC2/TiC/TiSi2 composites at up to 1550° C was studied using in‐situ neutron diffraction. The role of TiC and TiSi2 on the thermal stability of Ti3SiC2 during vacuum annealing is discussed. TiC reacts with TiSi2 between 1400–1450°C to form Ti3SiC2. Above 1400° C, decomposition of Ti3SiC2 into TiC commenced and the rate increased with increased temperature and dwell time. Furthermore, the activation energy for the formation and decomposition of Ti3SiC2 was determined. © 2009 American Institute of Physics
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    Effect of chromium-doping on the crystallization and phase stability in anodized TiO2 nanotubes
    (2013-04-08) Low, IM; Albetran, H; De La Prida, V; Manurung, P; Ionescu, M
    Production of limitless hydrogen fuel by visible light splitting of water using the photoelectrochemical technology is cost-effective and sustainable. To make this an attractive viable technology will require the design of TiO 2 photocatalyst capable of harnessing the energy of visible light. One possible solution is the doping of TiO2 to reduce its band gap. In this paper, the effect of Cr-doping by ion-implantation on the crystallisation and phase stability of TiO2 nanotubes at elevated temperature is described. The effect of Cr-doping on the resultant microstructures, phase changes and composition depth profiles are discussed in terms of synchrotron radiation diffraction, scanning electron microscopy, and ion-beam analysis by Rutherford backscattering spectrometry. © The American Ceramic Society
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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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    Effect of vacuum annealing on the thermal stability of Ti3SiC2/TiC/TiSi2 composites
    (The Australian Ceramic Society, 2009-01-01) Pang, WK; Low, IM; O’Connor, BH; Studer, AJ; Peterson, VK; Palmquist, JP
    Titanium silicon carbide (Ti3SiC2) possesses a unique combination of properties of both metals and ceramics, for it is thermally shock resistant, thermally and electrically conductive, damage tolerant, lightweight, highly oxidation resistant, elastically stiff, and mechanically machinable. In this research, the effect of high vacuum annealing on the phase stability and phase transitions of Ti3SiC2/TiC/TiSi2 composites up to 1550°C was studied using in-situ neutron diffraction. The role of TiC and TiSi2 on the thermal stability of Ti3SiC2 during vacuum annealing is discussed. TiC reacts with TiSi2 between 1400-1450°C to form Ti3SiC2. Above 1400°C, decomposition of Ti3SiC2 into TiC commenced and the rate increased with increased temperature and dwell time. Furthermore, the activation energy for the formatiTitanium silicon carbide (Ti3SiC2) possesses a unique combination of properties of both metals and ceramics, for it is thermally shock resistant, thermally and electrically conductive, damage tolerant, lightweight, highly oxidation resistant, elastically stiff, and mechanically machinable. In this research, the effect of high vacuum annealing on the phase stability and phase transitions of Ti3SiC2/TiC/TiSi2 composites up to 1550°C was studied using in-situ neutron diffraction. The role of TiC and TiSi2 on the thermal stability of Ti3SiC2 during vacuum annealing is discussed. TiC reacts with TiSi2 between 1400-1450°C to form Ti3SiC2. Above 1400°C, decomposition of Ti3SiC2 into TiC commenced and the rate increased with increased temperature and dwell time. Furthermore, the activation energy for the formation and decomposition of Ti3SiC2 was determined. on and decomposition of Ti3SiC2 was determined. © 2009, The Australian Ceramic Society
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    Fabrication and properties of recycled cellulose fibre-reinforced epoxy composites
    (Taylor & Francis, 2012-04-02) Low, IM; Somers, J; Kho, HS; Davies, IJ; Latella, BA
    Epoxy matrix composites reinforced with recycled cellulose fibre (RCF) were fabricated and characterized with respect to their flexural and impact properties. Reinforcement of the epoxy by RCF resulted in a significant increase in the strain at failure, fracture toughness and impact toughness but only a moderate increase in flexural strength and flexural modulus. The effect of accelerated exposure to seawater on the flexural and impact properties was also investigated. The salient toughening mechanisms and crack-tip failure processes were identified and discussed in light of observed microstructures, in particular the orientation of RCF sheets to the applied load. © 2020 Informa UK Limited
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    High temperature diffraction studies of in-situ crystallization of nanostructured TiO2 photocatalysts
    (The Ameican Ceramic Society, 2012-01-01) Low, IM; Pang, WK; Prida, VDL; Vega, V; Kimpton, JA; Ionescu, M
    The in-situ crystallization of anatase and rutile on chemically-treated Ti-foils in the temperature range 20-900 degrees C has been investigated using synchrotron radiation diffraction and x-ray diffraction. The processing methodology has a profound influence on the morphology, crystallite size and growth rate of nanostructured TiO2. The anatase formed was metastable and transformed to rutile at similar to 800 degrees C. Increasing the temperature from 400 to 900 degrees C caused the sharpening of anatase (101) peaks and resulted in a concomitant coarsening in crystallite size. The surface of annealed samples exhibited TiO2 nanorods, nanowires or nanotubes depending on the processing method. Ion-beam analysis has indicated the existence of composition gradation within the annealed TiO2 samples at the near-surface. © 2012, The American Ceramic Society.
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    High-temperature thermal stability of Ti2AlN and Ti4AlN3: a comparative diffraction study
    (Elsevier, 2011-01) Low, IM; Pang, WK; Kennedy, SJ; Smith, RI
    The susceptibility of Ti2AlN and Ti4AlN3 to high-temperature thermal dissociation in a dynamic environment of high-vacuum has been investigated using in situ neutron diffraction. Under high vacuum, these ternary nitrides decomposed above 1400°C through the sublimation of Al, and possibly Ti, to form a surface coating of TiNx (0.5 ≤ x ≤ 0.75). The kinetics of isothermal phase decomposition were modelled using the Avrami equation and the Avrami exponents (n) of isothermal decomposition of Ti2AlN and Ti4AlN3 were determined to be 0.62 and 0.18, respectively. The characteristics of thermal stability and phase transitions in Ti2AlN and Ti4AlN3 are compared in terms of the rate of decomposition, phase relations and microstructures. © 2010, Elsevier Ltd.
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    In situ diffraction study of thermal decomposition in Maxthal Ti2AlC
    (Elsevier, 2011-01-05) Pang, WK; Low, IM; O'Connor, BH; Peterson, VK; Studer, AJ; Palmquist, JP
    The thermal stability of Ti2AlC at elevated temperature (1000–1550°C) in vacuum has been investigated using in situ neutron diffraction. At temperatures above 1400°C, Ti2AlC became unstable and began to decompose via sublimation of Al, resulting in a porous surface layer of TiCx being formed. The apparent activation energy for Ti2AlC decomposition was determined to be 85.7 ± 2.6 kJ mol−1. The kinetics of isothermal phase decomposition was modelled using least-squares linear regression fitting and the Avrami equation. The corresponding least-squares regression exponent (R2) and Avrami constants (k and n) for isothermal decomposition were determined to be 0.89, 0.268 min−n and 0.1, respectively. © 2011, Elsevier Ltd.
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    In situ diffraction study on decomposition of Ti2AlN at 1500–1800°C in vacuum
    (Elsevier, 2010-11-25) Pang, WK; Low, IM; Kennedy, SJ; Smith, RI
    The susceptibility of Ti2AlN to thermal dissociation at 1500–1800°C in high-vacuum has been studied using in situ neutron diffraction. Above 1500°C, Ti2AlN decomposed to TiNx primarily through the sublimation of aluminium (Al). The kinetics of isothermal phase decomposition at 1550°C was modelled using a modified Avrami equation. An Avrami exponent (n) of 0.338 was determined, indicative of the highly restricted out-diffusion of Al between the channels of Ti6N octahedra. The characteristics of thermal stability and phase transition in Ti2AlN are discussed. Characterisation of surface compositions and examination of cross-sectional microstructures of decomposed Ti2AlN, using synchrotron radiation diffraction and SEM, respectively, verify the findings of the neutron diffraction; that Ti2AlN decomposes to TiNx at the surface primarily via the sublimation of Al from grain boundaries. © 2010, Elsevier Ltd.
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    In situ neutron diffraction investigation on the phase transformation sequence of kaolinite and halloysite to mullite
    (Elsevier B. V., 2006-11-15) Tezuka, N; Low, IM; Davies, IJ; Prior, MJ; Studer, AJ
    “Kaolin” is a major raw material for the fabrication of conventional ceramics. In this work the authors have investigated the thermal phase transformation of mullite from two different types of kaolin (kaolinite and halloysite), with or without alumina matrix constraint, during heating up to 1500 °C and then cooling using in situ neutron diffraction. Mullitization was initiated upon heating to 1200 °C for all specimens and followed spinel formation at 1100 °C. Above this temperature, however, evolution of the main phases, i.e., mullite, cristobalite and corundum, was influenced by the presence of impurities, initial type of silica, and alumina constraint. The relative amount of mullite was largest for the pure kaolinite specimen, particularly during heating, and this was attributed to the presence of a glassy phase. However, kaolinite with alumina suppressed the crystallization of cristobalite from the glassy phase upon cooling due to a reaction between alumina and amorphous silica, consequently resulting in an amount of mullite as for the pure kaolinite specimen (approximately 65 wt%). Halloysite was less active in terms of mullitization due to the lower level of initial impurities and greater amount of cristobalite, particularly for the alumina-constrained specimen. However, the final amount of mullite derived from the pure halloysite specimen was similar to that as from the kaolinite specimen. Crown Copyright © 2006 Published by Elsevier B.V.
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    In situ neutron diffraction study on the effect of aluminium fluoride on phase transformation of mullite from alumina/clay
    (John Wiley & Sons Inc, 2007-09-16) Tezuka, N; Low, IM; Davies, IJ; Alecu, I; Stead, R; Avdeev, M; Mehrtens, EG; Latella, BA
    The effect of aluminium fluoride (AIF3) on the phase transformation sequence of mullite (3AI2032Si02) from two different types of kaolin (kaolinite and halloysite) (AI2Si20s(OH)4-2H20) within an alumina (A1203) matrix for a temperature range of 20 - 1500 C was investigated using in situ neutron diffraction. Samples containing a mixture of A1F3 (0 - 5 wt%), AI203 and kaolin were heated up to 1500 C and then furnace cooled. During the heating procedure, one hour neutron diffraction scans were conducted at 600, 900, 1100, 1200, 1300 and 1400 C, followed by six consecutive one hour scans at 1500 C and finally a one hour scan at room temperature upon cooling. The diffraction patterns collected between 1100 and 1500 C were analyzed by Rietveld analysis. The observed phase transformations exhibited a typical sequence found inclay/alumina ceramics. Corundum, mullite and cristobalite were observed. A common feature among the specimens containing different amounts of AIF3 and kaolin was that the content of corundum decreased as the amount of mullite increased, whilst the cristobalite content tended to peak near the temperature where the amounts of corundum and mullite were approximately equal. The mullitization temperature was reduced as the AIF3 content increased for both kaolinite and halloysite. The presence of AIF3 appeared to reduce the onset temperature for mullite nucleation, which is at a much lower temperature compared to that of grain growth. However, AIF3 also seemed to lower densification. Likewise mechanical properties of the resulting specimens were determined. © MS&T07
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    In-situ neutron diffraction investigation on the phase transformation sequence of kaolinite and halloysite to mullite
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Tezuka, N; Low, IM; Davies, IJ; Prior, MJ; Studer, AJ
    “Kaolin” is a major raw material for the fabrication of conventional ceramics. Whilst kaolin has been thoroughly studied in the past decades with regards to its application as conventional ceramics there has been renewed interests in the conversion of kaolin to mullite (3Al2O3,2SiO2) with purpose of furthering the understanding of processing advanced ceramics with high strength, toughness, and thermal stability. One of the advantages of kaolin as a starting material is the needle-like morphology of mullite that is obtained by the transformation sequence at elevated temperature: kaolin —> metakaolin —> Al-Si spinel —> primary mullite (2Al203.SiO2) —> secondary mullite (3Al2O3.2SiO2). The ratio of Al203/SiO2 in mullite is considered to change by the replacement of Al and Si atoms in the tetrahedral positions. However, the in-situ transformation of primary to a secondary mullite has not been investigated in detail. This paper investigates the thermal phase transformation of mullite from two different types of kaolin (kaolinite and halloysite) with or without AIZO3 matrix constraint through the heating and cooling process by in-situ neutron diffraction. The effects of starting materials and heat treatment on the mullitisation process, especially in terms of primary —> secondary mullite evolution, are highlighted and discussed. © 2005 The Authors
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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.
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    Mapping of elemental composition in air-oxidized Ti3SiC2
    (Australian Ceramic Society, 2008-01-01) Pang, WK; Low, IM; Prince, KE; Atanacio, AJ
    Depth-profiling of elemental composition at the near surface of air-oxidized Ti3SiC2 was studied by secondary ion mass spectrometry (SIMS). The duplex microstructure of oxides formed at air-oxidized Ti3SiC2 surface was observed which consisted of an outer uniform layer of rutile-TiO2 and an inner graded layer of TiO2 and SiO2. The thickness of oxide scales increased with an increase in temperature. Ti3SiC2 is resistant to oxidation in air at up to 1100 degrees C. Copyright © 2008 Australian Ceramic Society.
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    Study of high-temperature thermal stability of MAX phases in vacuum
    (American Ceramic Society, 2010-01-28) Low, IM; Pang, WK; Kennedy, SJ; Smith, RI
    The susceptibility of two MAX phases (Ti2AlN and Ti 4AlN3) to high-temperature thermal dissociation in a dynamic environment of high-vacuum has been investigated using in-situ neutron diffraction. In high vacuum, these phases decomposed above 1400°C through the sublimation of Ti and Al elements, forming a surface coating of TiN. The kinetics of isothermal phase decomposition was modelled using the Avrami equation and the Avrami exponent (n) of isothermal decomposition of Ti 2AlN and Ti4AlN3 was determined to be 0.62 and 0.18 respectively. The characteristics of thermal stability and phase transitions in Ti2AlN and Ti4AlN3 are compared and discussed.
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    Synthesis and characterisation of ion-implanted epoxy composites for x-ray shielding
    (Elsevier Science BV, 2012-09-15) Azman, NZN; Siddiqui, SA; Ionescu, M; Low, IM
    The epoxy samples were implanted with heavy ions such as tungsten (W), gold (Au) and lead (Pb) to investigate the attenuation characteristics of these composites. Near-surface composition depth profiling of ion-implanted epoxy systems was studied using Rutherford Backscattering Spectroscopy (RBS). The effect of implanted ions on the X-ray attenuation was studied with a general diagnostic X-ray machine with X-ray tube voltages from 40 to 100 kV at constant exposure 10 mAs. Results show that the threshold of implanted ions above which X-ray mass attenuation coefficient, mu(m), of the ion-implanted epoxy composite is distinguishably higher than the mu(m), of the pure epoxy sample is different for W, Au and Pb. © 2012, Elsevier Ltd.