Browsing by Author "Cassidy, DJ"
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- ItemCrystallization of TiO2 powders and thin films prepared from modified titanium alkoxide precursors(Wiley-Blackwell, 2008-06) Karatchevtseva, I; Cassidy, DJ; Zhang, Z; Triani, G; Finnie, KS; Cram, SL; Barbé, CJThe modification of titanium alkoxides by chemical reactions with ligands yields complexes or molecular clusters that are substantially different from those of the parent alkoxides. In this study, we investigate the structural evolution of powders and thin films prepared from two titanium oxo-alkoxyacylate clusters with different oxo-core structures [Ti6(μ3-O)2(μ2-O)2](CH3COO)8(μ2-OiPr)2(OiPr)6 and [Ti6(μ3-O)6](μ-RCOO)6(OiPr)6 ([6,4] and [6,6], respectively) as a function of annealing temperature. The structural evolution of powders and thin films prepared from the corresponding parent alkoxide Ti(OiPr)4 (TiP) were also investigated for comparison. In all powders, the amorphous-to-anatase transformation occurred upon heating to 400°C. In sharp contrast, the anatase-to-rutile transformation of the powder prepared from the [6,6] cluster was significantly inhibited compared with the conventionally derived powder, with no rutile being detected even after annealing at 800°C for 1 h. This was attributed to the small crystallite size in the [6,6]-derived powder, which is lower than the critical size previously reported for the anatase-to-rutile transformation in similar sol–gel-derived materials. In thin films, the amorphous-to-anatase phase transition also occurred at temperatures as low as 400°C for coatings deposited from conventional TiP precursor and [6,4] cluster solutions. However, in contrast to the corresponding powders no rutile nucleation occurred even at 800°C in either film. © 2008, Wiley-Blackwell.
- ItemHigh-temperature study of CaZrTi2O7(Elsevier, 1992-08-02) Vance, ER; Cassidy, DJ; Ball, CJ; Thorogood, GJPreviously reported anomalous thermal expansion effects in the 1200–1500°C range for hot-pressed CaZrTi2O7 were shown to be due to irreversible bloating effects, from occluded gases. X-ray diffraction and differential thermal analysis of ordered CaZrTi2O7 did not reveal evidence of a solid-state transformation at temperatures up to 1450°C. © 1992 Elsevier
- ItemImmobilisation of cations and anions in geopolymers(Materials Science and Technology (MS&T), 2007-09-16) Vance, ER; Perera, DS; Aly, Z; Walls, P; Zhang, YJ; Cassidy, DJ; Griffith, CS
- ItemIncorporation of uranium in zirconolite (CaZrTi2O7)(John Wiley & Sons, Inc, 2002-07) Vance, ER; Lumpkin, GR; Carter, ML; Cassidy, DJ; Ball, CJ; Day, RA; Begg, BDUp to 0.15 formula unit (f.u.) of U4+ incorporated in the Zr site of zirconolite by firing CaUxZr(1−x)Ti2O7 compositions in argon at 1400°C allows retention of the 2M polytype. Further U4+ substitution for Zr, up to 0.4 f.u., produces the 4M polytype (containing ∼0.4 f.u. of U) plus the 2M polytype containing 0.15 f.u. of U. The pyrochlore structure (containing 0.6 f.u. of U) forms in conjunction with the 4M polytype at U contents of 0.4 f.u. up to 0.7 f.u. Higher U contents give the pyrochlore structure, but the solid-state reactivity of even alkoxide-based preparations becomes increasingly poor for x > ∼0.7 and hot pressing in graphite dies at ∼1250°C is necessary to achieve near single-phase pyrochlore structures for x= 1. When samples of CaUxZr1−xTi2O7 stoichiometry (x= 0.1 and 0.2) are oxidized at 1400°C in air, diffuse reflectance spectroscopy (DRS) shows evidence for U5+ formation at the expense of U4+ via enhanced absorption bands, ∼50 nm in half-width, near 970 and 1500 nm and correspondingly weakened absorption at 1150 and 1660 nm. Weight gains consistent with complete oxidation of U4+ to U5+ are observed when finely powdered argon-fired samples with x= 0.1 and 0.4 are heated in air to 1200°C. Evidence for U valence states higher than +4 in both argon- and air-heated materials containing charge compensators to encourage U5+ or U6+ formation was also derived from DRS (showing U5+ in particular), and XANES. DRS shows weak absorption bands attributable to U4+ in zirconolites containing ∼0.2 f.u. of U incorporated in the Ca site via Mg or Al substitutions in the Ti sites, with the spectrum being closely but not exactly similar to that attributed to U4+ in the Zr site. Zirconolite and pyrochlore compositions which are melted at 1500° or 1550°C in argon and furnace-cooled yield broadly similar phase assemblages to the corresponding sintered materials, but there is evidence of incongruent melting in all materials. © 2002 The American Ceramic Society
- ItemLow temperature bonding of ceramics by sol-gel processing(Springer Nature, 2001-12) Barbé , CJ; Cassidy, DJ; Triani, G; Latella, BA; Mitchell, DRG; Finnie, KS; Bartlett, JR; Woolfrey, JL; Collins, GASol-gel bonds were produced between smooth, clean silicon or polycrystalline alumina substrates by spin-coating solutions containing partially hydrolysed silicon alkoxides onto both substrates. The two coated substrates were assembled and the resulting sandwich was fired at temperatures ranging from 300 to 600°C. The influence of the sol-gel chemistry on the film microstructure and interfacial fracture energy was investigated using a wide range of techniques, including ellipsometry, FTIR, TG-DTA, rheology, TEM and micro-indentation. For silicon wafers, an optimum water-alkoxide molar ratio of 10 and hydrolysis water pH of 2 were found. Such conditions led to relatively dense films (>90%), resulting in bonds with significantly higher fracture energy (3.5 J/m2) than those obtained using classical water bonding (typically 1.5 J/m2). Aging of the coating solution was found to decrease the bond strength. Poly-crystalline alumina substrates were similarly bonded at 600°C; the optimised silica sol-gel chemistry yielded interfaces with fracture energy of 4 J/m2. © 2000 Kluwer Academic Publishers.
- ItemNanostructural evolution of titania-based materials using modified titanium precursors.(Wiley-Blackwell, 2009-09) Arrachart, G; Cassidy, DJ; Karatchevtseva, I; Triani, GTitanium ethoxide [Ti(OEt)(4)] was modified with aminobenzoic acid (AB) or aminosalicylic acid (AS) in order to control the hydrolysis and condensation rates, and to allow the preparation of organic-inorganic hybrid materials. A suite of complementary techniques, including Fourier transform infrared spectroscopy, NMR, SEM, thermogravimetric analysis, and X-ray diffraction, were used to elucidate the effects of incorporating an organic functional group into the precursor chemistry and its subsequent affect on the structure and morphology of the resultant hybrid material. The annealing behavior of the resulting hybrid titanium base materials was also investigated. Our studies show that both amino acid organic ligands, AB and AS, chemically bounded to the titanium complex, effect the precursor reactivity, specifically the hydrolysis and polycondensation reactions, which control the evolution and formation of the nanohybrid-based titania material. Following sol-gel processing, the nanohybrid materials are amorphous, due to the incorporation of the organic component. The phase transition (amorphous-anatase-rutile) observed during annealing from 25 degrees to 800 degrees C show subtle differences in the crystallization behavior, which are associated with the nature of the organic ligand. © 2009, Wiley-Blackwell.
- ItemPerlite waste as a precursor for geopolymer formation(The Australian Ceramic Society, 2009) Vance, ER; Perera, DS; Imperia, P; Cassidy, DJ; Davis, J; Gourley, JTWaste perlite can be reacted with alkaline solutions to form crystalline zeolite 4A and other minor crystalline phases. The fine majority fraction of the waste was fairly reactive and the coarse fraction largely acted as a filler. This geopolymer had poor compressive strength, but when perlite was used in conjunction with flyash, geopolymers of acceptable mechanical properties could be made. Perlite shows significant reaction with 10 Mol/L NaOH solution at ˜70°C, with hydroxysodalite appearing as a reaction product. © 2009, The Australian Ceramic Society
- ItemSynthesis and characterisation of nanocomposite materials prepared by dispersion of functional TiO2 nanoparticles in PMMA matrix(Royal Society of Chemistry, 2011-07-29) Arrachart, G; Karatchevtseva, I; Heinemann, A; Cassidy, DJ; Triani, GComposite powders and thin films composed of poly(methyl methacrylate) (PMMA) and functionalised titania nanoparticles are successfully prepared by in situ bulk co-polymerisation using benzoyl peroxide (BPO) as the initiator. The functionalised titania nanoparticles are synthesised by an arrested hydrolysis of Ti(OiPr)4 with either undecylenic (UA) or undecenylphosphonic (UPA) acids used as the organic templates with the long hydrocarbon chains and functional (terminal double bond) groups. Surface-modified TiO2 nanoparticles could be easily dispersed in organic solvent due to the long hydrocarbon chain surrounding the titanium core, and engaged as a co-monomer in polymerisation with the MMA due to the presence of a terminal double bond. TEM and small angle X-ray scattering (SAXS) data presented support the homogeneous and consistent distribution of inorganic phase within the PMMA matrix, with the larger titania nanoparticles detected when the UPA was employed to modify a TiO2 nanoparticle. This is attributed to the UPA greater binding affinity towards the TiO2 surfaces and therefore particles aggregation to some extent. © 2011 Royal Society of Chemistry
- ItemSynthesis and characterization of functionalized silica-based nanohybrid materials for oxyanions adsorption(American Chemical Society, 2010-06-01) Karatchevtseva, I; Astoux, M; Cassidy, DJ; Yee, P; Bartlett, JR; Griffith, CSThis study investigates the structural evolution of a series of nanohybrid powders and coatings synthesized by direct co-condensation of amino-functionalized alkyltrialkoxysilanes and tetraalkoxysilanes with an aromatic carboxylic acid (trimesic acid, TMA) as a structure directing agent. Fourier transform infrared spectroscopy (FTIR) and 13C CP-MAS NMR results have suggested the formation of secondary (−CO−NH−) amide linkages upon interaction of TMA with the amino functionalized silane thus creating a “scaffold” around which the silica network is formed and also assisting in more homogeneous distribution of nitrogen sites within the nanohybrid structure. Functionalized silica powders were investigated for their potential to remove toxic oxyanions from mildly acidic or basic solutions. The uptake of Mo(VI), Se(VI), and Cr(VI) oxyanions was investigated as a function of the nanohybrid composition, oxyanion concentration, and solution pH using laser diffraction particle sizing, gas adsorption, and various spectroscopic techniques. The adsorption data obtained for Mo and Se could be adequately described by Langmuir adsorption isotherms, while the Freundlich isotherm is employed to fit the adsorption data for Cr. An easily accessible processing window (of pH, aging time, etc.) has been identified allowing production of continuous and uniform thin nanohybrid coatings on silicon and glass substrates. These coatings were tested as chemical barriers against Mo leaching from specially prepared Mo-doped glass. Leaching studies were conducted over 200 days in water at 90°C and the Mo leaching from coated and uncoated samples compared. © 2010, American Chemical Society
- ItemSynthesis of nanoporous silicon carbide via the preceramic polymer route(Elsevier, 2009-02-15) Maddocks, AR; Cassidy, DJ; Jones, AS; Harris, ATNanoporous silicon carbide materials were prepared by the pyrolysis of the preceramic polymer, polycarbosilane (PCS), with and without the addition of an inert filler (nano- and micron-sized silicon carbide powders). Hydrosilylation crosslinking of PCS with divinylbenzene prior to pyrolysis appeared to have little influence on the development of micro- and mesoporosity. Maximum micropore volumes were 0.28 cm3 g−1 for non-crosslinked PCS and 0.25, 0.33 and 0.32 cm3 g−1 for PCS crosslinked with 2, 6 and 10 wt.% DVB respectively. Micropore volumes decreased under hydrothermal conditions to 0.03 cm3 g−1 for non-crosslinked and 0 cm3 g−1 for crosslinked PCS. Porosity was also lost at temperatures above 700°C. The addition of nano-sized SiC powders to PCS prior to pyrolysis maintained mesoporosity to temperatures of 1200°C, however, micron-sized SiC powders did not maintain porosity above 800°C. The modal pore size in pellets formed by compressing micron-sized powders with the preceramic polymer was 5 μm compared to 30 nm when nano-sized powders were used. © 2009, Elsevier Ltd.
- ItemThermal expansion of solutions of deuteromethane in fullerite C60 at low temperatures. Isotopic effect(American Institute of Physics, 2009-03) Dolbin, AV; Vinnikov, NA; Gavrilko, VG; Esel'son, VB; Manzheliĭ, VG; Gadd, GE; Moricca, SA; Cassidy, DJ; Sundqvist, BThe thermal expansion of CD4 solutions in the orientational glass C60 with molar concentration of deuteromethane 20 and 50% has been investigated in the temperature range 2.5–23 K. The orientational glass CD4–C60 undergoes a first-order phase transition in the temperature interval 4.5–55 K. This transition is manifested as hysteresis of the linear thermal expansion coefficient α as well as maxima in the temperature dependences α(T) and τ1(T), where τ1 is the characteristic thermalization time of the experimental samples. The characteristic re-orientation times of the C60 molecules and the characteristic phase transformations occurring in the experimental solutions are determined. The results of the present study are compared with the results of a similar study of the solution CH4–C60. It is concluded that tunneling rotation of the CH4 and CD4 molecules occupying interstitial positions in the fullerite C60 lattice occurs. © 2009, American Institute of Physics