Browsing by Author "Blackford, MG"

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    Alkaline hydrothermal kinetics in titanate nanostructure formation.
    (Springer, 2011-01) Morgan, DL; Triani, G; Blackford, MG; Raftery, NA; Frost, RL; Waclawik, ER
    In this study, the mechanism of precursor dissolution and the influence of kinetics of dissolution on titanate nanotube formation were investigated. This comparative study explored the dissolution kinetics for the case of commercial titania powders, one composed of predominantly anatase (>95%) and the other rutile phase (>93%). These nanoparticle precursors were hydrothermally reacted in 9 mol L−1 NaOH at 160°C over a range of reaction times of between 2 and 32 h. The high surface area nanotube-form product was confirmed using X-ray diffraction, FT-Raman spectroscopy, and transmission electron microscopy. The concentration of nanotubes produced from the different precursors was established using Rietveld analysis with internal and external corundum standardization to calibrate the absolute concentrations of the samples. Interpretation of the dissolution process of the precursor materials indicated that the dissolution of anatase proceeds via a zero-order kinetic process, whereas rutile dissolution is through a second-order process. The TiO2 nanostructure formation process and mechanism of TiO2 precursor dissolution was confirmed by non-invasive dynamic light scattering measurements. Significant observations are that nanotube formation occurred over a broad range of hydrothermal treatment conditions and was strongly influenced by the order of precursor dissolution. © 2011, Springer
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    ANSTO electron microscopy building
    (Australian Microscopy and Microanalysis Society, 2015-02-12) Blackford, MG
    Modern scanning and transmission electron microscopes are capable of extremely high-resolution performance. However, they must be installed in suitable laboratory environments to achieve their design specifications [1, 2]. Existing electron microscopy facilities at ANSTO are housed in a ~60 year old general-purpose building. The laboratory environment in which they are currently located compromises their performance due to external influences such as stray electromagnetic fields, acoustic and mechanical vibrations, high airflow, and excessive cooling water and air temperature variations. A building specifically designed and constructed to provide the optimum environment is nearing completion and will allow ANSTO’s considerable investment in electron microscopes to operate at their full potential thereby maximising their scientific impact. The facility will be suitable for future new generation high-end electron microscopes when current instruments are replaced over coming years. Consultation with staff at a number of similar facilities identified key design features required to optimise the instrument laboratory environment. These include independent vibration isolated ~1m thick fibre-reinforced concrete slabs for each laboratory, chilled ceiling panels for low air flow precision temperature control, minimal use of metal in the main building and location of air conditioning, electrical, chilled water and compressed gas facilities in a separate plant room. Laminated wooden portal frames support the outer structure of the main building. Instrument labs are constructed from concrete Besser blocks reinforced with fibreglass rod, which are also used to reinforce the corridor slabs. The building is divided into separate zones (Fig. 1) ranging from lowest environmental specifications in the entrance foyer/office area (orange), through progressively higher specifications in the service corridors, specimen preparation lab and air locks (yellow) to the most stringent specification in instrument labs (blue). Electrical wiring distribution is designed to minimise electromagnetic fields at the microscope column positions within each of the labs. Active field compensation is not being installed initially, however it can be retrofitted should the need arise. Construction is well advanced (Fig. 2) and should be completed by the end of February 2015. Relocation of the instruments is anticipated by the end of June 2015.
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    Aqueous chemical synthesis of Ln2Sn2O7 pyrochlore-structured ceramics
    (John Wiley and Sons, 2013-06-03) Kong, L; Karatchevtseva, I; Blackford, MG; Scales, N; Triani, G
    Pyrochlore-structured lanthanide stannate ceramic (Ln2Sn2O7) has been synthesized via a new complex precipitation method. A suite of characterization techniques, including FTIR, Raman, X-ray, and electron diffraction as well as nitrogen sorption were employed to investigate the structural evolution of the synthesized and calcined powder. Raman, XRD, and selected area electron diffraction results confirm the presence of the pyrochlore structure after calcination of the powder above 1200°C. TEM imaging shows fine crystallites gradually increased in size from approximately 100 nm to about 500 nm with higher calcination temperatures. Grain growth and powder densification upon increasing the calcination temperature was confirmed by nitrogen sorption results. This aqueous synthetic method provides a simple pathway for the preparation of homogeneous lanthanide stannate ceramics. © 2013, The American Ceramic Society.
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    Catalytic hydrogen production from ethanol over Rh-Pd/CeO2
    (American Chemical Society, 2008-04-06) Scott, M; Chiu, W; Blackford, MG; Idriss, H
    The work focus on the catalytic reactions for hydrogen production over a bimetallic catalytic system composed of small metallic clusters (of the order of 1nm size) dispersed on nanoparticles of cerium oxides. The catalytic process involves steam reforming of ethanol as well as water gas shift reaction. This type of catalysts has proved very active, selective and stable for the production of hydrogen under realistic conditions. Moreover at the temperature range of 700-800K no or traces of CO are seen. Detailed study indicates that the active sites of the catalyst are those at the interface between the metallic clusters and the reconstructed CeO2 surface.
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    Characterization and leaching behavior of plutonium-bearing Synroc-C
    (Cambridge University Press/Springer Nature, 1996-02-05) Smith, KL; Lumpkin, GR; Blackford, MG; Hambley, M; Day, RA; Hart, KP; Jostsons, A
    Synroc-C containing 10wt% simulated PW-4b-D HLW including 0.62 wt% 239Pu was subjected to MCC-1 type leach tests at 70°C in deionised water, silicate and carbonate leachates for 53 d and deionised water for 2472 d. The normalised total (i.e. unfiltered leachate + vessel wall) Pu leach rates in deionised water, silicate and carbonate leachates for periods up to 53 d were found to be of the order of 10-5, 10-4 and 10-4 g m-2 d-1 respectively. After 2472 d, the differential, normalised, Pu leach rate in deionised water dropped to ∼5 × 10-6 (total) and ∼5 × 10-8 (solution - after filtration through a 1000NMW filter) g m-2 d-1. SEM and AEM were used to characterise our starting material and investigate the secondary phases on the surfaces of leached Synroc-C discs. Calculated and measured normalised Pu leach rates are compared and the partitioning of Pu between zirconolite and perovskite is discussed. © Materials Research Society 1997
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    Characterization of nanocrystalline materials using different diffraction techniques
    (International Community for Composites Engineering, 2008-07-20) Kamarulzaman, N; Bustam, MA; Blagojevic, N; Elcombe, MM; Blackford, MG; Avdeev, M; Arof, AK
    No abstract available.
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    Charge compensation mechanisms for aliovalent impurities in perovskite and zirconolite
    (Australian and New Zealand Institutes of Physics, 1994-02-10) Vance, ER; Day, RA; Begg, BD; Blackford, MG
    As part of the chemical design of Synroc-type ceramics for the immobilisation of different high-level radioactive wastes from nuclear fuel reprocessing, it is necessary to understand the various possible charge compensation mechanisms which occur when up to tens of atomic percent of rare earths and actinides are incorporated in solid solution in perovskite (CaTiO3) and zirconolite (CaZrTi2O7). In particular the solid solution of Gd in the Ca site of perovskite and the incorporation of Nd, Ce, U, Np and Pu in the Ca and Zr sites of zirconolite have been studied by XRD, SEM, TEM, and XANES. The essential conclusions are that in formulations where charge compensating ions are made available, then this is the preferred mechanism for incorporation of these cations in Ca and Zr sites. However in formulations where such compensators are not made available, it is possible for charge compensation to take place via significant abundances of cation vacancies, or by the appearance of unexpected valence states stabilised by crystal-chemical forces. An example of the latter is the probable stabilisation of Ti3+ in Ti sites, and of trivalent Ce and actinides in Ca and Zr sites, even under quite oxidising conditions. A complication in these studies is the effect of prevailing or inherited redox conditions. Redox conditions influence phase abundances and compositions as they control the valencies of cations capable of more than one oxidation state. There is also an indication that reducing conditions can promote oxygen site deficiencies in some formulations. Other complicating factors relate to sample fabrication, arising from the need to make extremely chemically uniform phases having the desired composition. This requires prolonged heating at high temperatures to achieve complete solid-state reaction that may result in selective losses due to volatilisation. Incipient melting due to localised eutectic formation and the apparently straightforward task of efficient stoichiometric mixing on a 1 to 10 um scale are other problems which have had to be overcome in sample fabrication.
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    Chemistry and radiation effects of davidite
    (GeoScienceWorld, 2013-10-01) Lumpkin, GR; Blackford, MG; Colella, M
    Davidite (A1−xM21O38) samples from five different geological localities contain approximately 0.2 to 9.5 wt% UO2 (0.02 to 0.65 atoms per formula unit) and <0.1 to 1.3 wt% ThO2 (<0.01 to 0.09 atoms per formula unit). Maximum amounts of other notable cations include 3.7 wt% V2O3, 4.1 wt% Cr2O3, 2.5 wt% Y2O3, 5.6 wt% La2O3, 6.0 wt% Ce2O3, 4.0 wt% MnO, 2.4 wt% ZnO, 2.7 wt% SrO, and 4.9 wt% PbO. As a result of the variation in age and Th-U content, the calculated α decay dose ranges from ~0.2 to 44 × 1016 α/mg (~0.06 to 14.5 dpa). For samples with ages of 275–295 Ma, the critical dose for amorphization based on electron diffraction is ~0.8 × 1016 α/mg. Natural davidite is commonly altered to rutile, ilmenite, titanite, and other minor phases. © 2013, Mineralogical Society of America.
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    Crystal chemistry and structures of uranium-doped gadolinium zirconates
    (Elsevier, 2013-07-01) Gregg, DJ; Zhang, YJ; Zhang, ZM; Karatchevtseva, I; Blackford, MG; Triani, G; Lumpkin, GR
    A series of uranium-containing gadolinium zirconate samples have been fabricated at 1450 °C in oxidizing, inert and reducing atmospheres. X-ray diffraction, Raman spectroscopy and transmission electron microscopy have been utilized to confirm adoption of pyrochlore or defect fluorite structures. X-ray diffraction allowed determination of the bulk averaged structure while Raman spectroscopy and transmission electron microscopy were used to determine ordering at the microdomain scale. Diffuse reflectance, X-ray absorption near edge structure and X-ray photoelectron spectroscopies indicated a predominantly U6+ oxidation state for all the air-sintered samples, even when Ca2+ or A-site vacancies were incorporated to charge balance for U4+, a mixed U5+/U6+ oxidation state was found for samples sintered in argon, while a mixed U4+/U5+ oxidation state occurred for sintering under N2–3.5%H2. This demonstrates a degree of uranium oxidation state control through sintering conditions, and the potential of using gadolinium zirconates as host materials for uranium in nuclear waste applications.© 2013, Elsevier B.V.
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    Dissolution of Synroc in deionised water at 150°C
    (Materials Research Society (MRS)/Cambridge University Press/Springer Nature, 1996-02-15) Smith, KL; Colella, M; Thorogood, GJ; Blackford, MG; Lumpkin, GR; Hart, KP; Prince, KE; Loi, E; Jostsons, A
    Synroc containing 20 wt% simulated high level waste (HLW) was subjected to two sets of leach tests at 150°C where the leachant was and was not replaced during the test (replacement and non-replacement testing). The leachant was a KH-phthalate buffered solution (pH 4.2). Samples were characterised before and after leach testing using SEM, AEM and SIMS. Elemental concentrations in leachates were measured using ICP-MS. In concert with the findings of i) a dissolution study of perovskite in a flowing leachant and ii) a previous Synroc dissolution study (wherein Synroc containing 10 wt% simulated HLW was subjected to periodic replacement, leach testing in deionised water at 150°C), the results of this study show that when the leachant replacement frequency is varied from 7 d to the duration of the test, there is no effect on leach rate or leaching mechanisms. © Materials Research Society 1997
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    dLow temperature of formation of nickel germanide by reaction of nickel and crystalline germanium
    (Springer Nature, 2014-12) Algahtani, F; Leech, PW; Reeves, GK; Holland, AS; Blackford, MG; Thorogood, GJ; McCallum, JC; Johnson, BC
    The formation of nickel germanide has been examined over a range of low temperatures (200-400 °C) in an attempt to minimize the thermal budget for the process. Cross-sectional Transmission Electron Microscopy (TEM) was used to determine the texture of the germanide layer and the morphology and constituent composition of the Ge/NiGe interface. The onset and completion of reaction between Ni and Ge were identified by means of a heated stage in combination with in-situ x-ray diffraction (XRD) measurements. The stages of reaction were also monitored using measurements of sheet resistance of the germanides by the Van der Pauw technique. The results have shown that the minimum temperature for the initiation of reaction of Ni and Ge to form NiGe was 225 °C. However, an annealing temperature > 275 °C was necessary for the extensive (and practical) formation of NiGe. Between 200 and 300 °C, the duration of annealing required for the formation of NiGe was significantly longer than at higher temperatures. The stoichiometry of the germanide was very close to NiGe (1:1) as determined using energy dispersive spectroscopy (EDS).
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    Effect of B4C addition to MnO2 in a cathode material for battery applications.
    (Elsevier, 2010-01-01) Minakshi, M; Blackford, MG; Thorogood, GJ; Issa, TB
    Boron carbide (B4C) added manganese dioxide (MnO2) used as a cathode material for a Zn–MnO2 battery using aqueous lithium hydroxide (LiOH) as the electrolyte is known to have higher discharge capacity but with a lower average discharge voltage than pure MnO2 (additive free). The performance is reversed when using potassium hydroxide (KOH) as the electrolyte. Herein, the MnO2 was mixed with 0, 5, 7 and 10 wt.% of boron carbide during the electrode preparation. The discharge performance of the Zn|LiOH|MnO2 battery was improved by the addition of 5–7 wt.% boron carbide in MnO2 cathode as compared with the pure MnO2. However, increasing the additive to 10 wt.% causes a decrease in the discharge capacity. The performance of the Zn|KOH|MnO2 battery was retarded by the boron carbide additive. Transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy analysis (EDS) results show evidence of crystalline MnO2 particles during discharging in LiOH electrolyte, whereas, manganese oxide particles with different oxygen and manganese counts leading to mixture of phases is observed for KOH electrolyte which is in agreement with X-ray diffraction (XRD) data. The enhanced discharge capacity indicates that boron atoms promote lithium intercalation during the electrochemical process and improved the performance of the Zn|LiOH|MnO2 battery. This observed improvement may be a consequence of B4C suppressing the formation of undesirable Mn(III) phases, which in turn leads to enhanced lithium intercalation. Too much boron carbide hinders the charge carrier which inhibits the discharge capacity. © 2009, Elsevier Ltd.
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    Effect of gold loading and TiO2 support composition on the activity of Au/TiO2 photocatalysts for H-2 production from ethanol-water mixtures
    (Elsevier, 2013-09-01) Jovic, V; Chen, WWT; Sun-Waterhouse, D; Blackford, MG; Idriss, H; Waterhouse, GIN
    This paper systematically compares the activity of Au/TiO2 photocatalysts (Au loadings 0–10 wt.%) for H2 production from ethanol–water mixtures under UV excitation. Degussa P25 TiO2 was used as the support phase. TEM analyses revealed that the average Au nanoparticle size at all loadings was 5 ± 2 nm, with the Au nanoparticles preferentially located at the interfacial sites between TiO2 crystallites. XRD, XRF, XPS, and UV–Vis measurements established that metallic Au was the only gold species on the surface of the photocatalysts. The Au/TiO2 photocatalysts showed an intense absorption maximum centred around 560–570 nm due to the localised surface plasmon resonance (LSPR) of the supported gold nanoparticles. Photoluminescence measurements revealed that gold nanoparticles effectively suppress electron–hole pair recombination in TiO2, even at low Au loadings. All of the Au/TiO2 photocatalysts displayed high activity for H2 production from ethanol–water mixtures under UV irradiation, with the highest activities observed in the Au loading range 0.5–2 wt.% (H2 production rate 31–34 mmol g−1 h−1). In order to deconvolute the role of the P25 TiO2 support in promoting H2 production, anatase and rutile nanoparticles were isolated from P25 TiO2 by selective chemical dissolution and then functionalised with gold nanoparticles (3 wt.% loading, size 5 ± 2 nm). The H2 production activity of the resulting Au/anatase and Au/rutile photocatalysts was 22 and 10 mmol g−1 h−1, respectively, and substantially lower than the corresponding Au/P25 TiO2 photocatalyst (32 mmol g−1 h−1). The data provide strong evidence that synergistic electron transfer between the TiO2 polymorphs and supported Au nanoparticles is responsible for the high rates of H2 production observed in the Au/P25 TiO2 system. The interface between anatase and rutile crystallites, where gold nanoparticles preferentially deposit, is identified as a photocatalytic ‘hot spot’ for H2 production. High Au loadings reduce the efficiency of such ‘hot spots’. © 2013, Elsevier Inc.
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    Effect of TiS2 additive on LiMnPO4 cathode in aqueous solutions
    (American Chemical Society, 2010-11-18) Minakshi, M; Pandey, A; Blackford, MG; Ionescu, M
    Incorporation of TiS2 additive by physical admixture into the LiMnPO4 cathode leads to modification of the electrochemical performance of the cathode, such as an improved delithiation and lithiation mechanism. Cyclic voltammetry suggests that the TiS2 additive suppresses proton deinsertion/insertion mechanism and does not contribute directly to the reduction/oxidation reactions of the LiMnPO4 working electrode. © 2010, American Chemical Society
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    Electrochemical characteristics of B4C or BN added MnO2 cathode material for alkaline batteries
    (Elsevier, 2010-10-01) Minakshi, M; Blackford, MG
    Boron compounds generally produce a battery with high energy density. Since boron is an excellent conductor of electricity a battery with a high power density can also be achieved. With this objective, the electrochemical characteristics of boron carbide (B4C) added manganese dioxide (MnO2) for use as a cathode in alkaline battery were investigated during the discharge–charge process. Results of electrochemical measurements, X-ray diffraction and transmission electron microscopy show that boron aids the formation of lithium intercalated MnO2 (LixMnO2) during discharge with some degree of reversibility, however, capacity fade and a steep voltage profile is observed. The addition of boron nitride (BN) improved the discharge performance and characteristics of the cell are also compared and discussed. © 2010, Elsevier Ltd.
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    An electron energy loss spectroscopy and electron diffraction study of the Pmnb polymorph of Li2MnSiO4
    (Elsevier, 2013-02-25) Gummow, RJ; Blackford, MG; Lumpkin, GR; He, Y
    The Mn valency and the crystallinity of Li2MnSiO4 cathodes (Pmnb form) were examined with electron energy-loss spectroscopy (EELS) and selected area electron diffraction (SAED) both before and after electrochemical lithium extraction. A decrease in the crystallinity of the delithiated charged cathode particles compared to the as-prepared material was observed. The decrease in crystallinity varied from particle to particle. EELS analysis showed that the non-uniform decrease in crystallinity was due to a non-uniform extraction of lithium from the particles. The observed decrease in discharge capacity of the Pmnb polymorph of Li2MnSiO4 with cycling was attributed to the progressive loss of crystallinity and the structural collapse of Li diffusion pathways. © 2012, Elsevier B.V.
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    Fe speciation in geopolymers with Si/Al molar ratio of ~2.
    (Elsevier, 2007-05-01) Perera, DS; Cashion, JD; Blackford, MG; Zhang, Z; Vance, ER
    The speciation of Fe was studied in metakaolin-based geopolymers to which Fe was added as ferric nitrate solution or freshly precipitated ferric hydroxide. From Mössbauer and near-edge X-ray absorption spectroscopies, coupled with X-ray diffraction and electron microscopy, it was concluded that in as-cured geopolymers the Fe was present in octahedral sites, either as isolated ions in the geopolymer matrix or as oxyhydroxide aggregates which had not reacted with the starting geopolymer components. For material to which iron nitrate was added, heating to 900°C allowed the formation of nepheline and a glass, both of which contained tetrahedrally coordinated, substituted Fe3+. © 2007, Elsevier Ltd.
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    Gd2Zr2O7 and Nd2Zr2O7 pyrochlore prepared by aqueous chemical synthesis
    (Elsevier, 2013-12-01) Kong, L; Karatchevtseva, I; Gregg, DJ; Blackford, MG; Holmes, R; Triani, G
    Pyrochlore structured Gd2Zr2O7 and Nd2Zr2O7 are produced via complex precipitation processing. A suite of characterization techniques, including FTIR, Raman, X-ray and electron diffraction, TEM, SEM as well as nitrogen sorption are employed to investigate the structural and grain size evolution of the synthesized and calcined powder. Results show that Gd2Zr2O7 with the pyrochlore structure are produced after calcination at 1400 °C for 12 h while Nd2Zr2O7 has already formed the pyrochlore structure at 1200 °C. This method allows the formation of dense materials at relatively low temperature, with bulk densities over 92% of the theoretical values achieved after sintering at 1400 °C for 50 h. This unique aqueous synthetic method provides a simple pathway to produce pyrochlore lanthanide zirconate without using either organic solvent and/or mechanical milling procedures, making the synthesis protocol an attractive potential scale-up production of highly refractory ceramics. © 2013, Elsevier Ltd.
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    Geopolymers for low-level waste immobilization
    (American Ceramic Society, 2006-10-15) Vance, ER; Blackford, MG; Hanna, JV; Aly, Z; Perera, DS
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    Heat source probe for measuring thermal conductivity in waste rock dumps.
    (Australian Atomic Energy Commission, 1985-10) Blackford, MG; Harries, JR
    The development and use of a heat source probe to measure the thermal conductivity of the material in a waste rock dump is described. The probe releases heat at a constant rate into the surrounding material and the resulting temperature rise is inversely related to the thermal conductivity. The probe was designed for use in holes in the dump which are lined with 50 mm i.d. polyethylene liners. The poor thermal contact between the probe and the liner and the unknown conductivity of the backfill material around the liner necessitated long heating and cooling times (>10 hours) to ensure that the thermal conductivity of the dump material was being measured. Temperature data acquired in the field were analysed by comparing them with temperatures calculated using a two-dimensional cylindrical model of the probe and surrounding material and the heat transfer code HEATRAN.