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Browsing Journal Articles by Subject "Acid neutralizing capacity"

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    Chemical and isotopic signatures of waters associated with the carbonation of ultramafic mine tailings, Woodsreef Asbestos Mine, Australia
    (Elsevier, 2016-10-15) Oskierski, HC; Dlugogorski, BZ; Oliver, TK; Jacobsen, GE
    Extensive carbonate crusts have formed on the tailings of the Woodsreef Asbestos Mine, sequestering significant amounts of CO2 directly from the atmosphere. The physico-chemical (pH, T, conductivity), chemical (cations, dissolved inorganic carbon (DIC)) and isotopic (δ2H, δ18O, δ13CDIC, F14C) signatures of waters interacting with the tailings and associated carbonate precipitates provide insight into the processes controlling carbonation. We observe two distinct evolutionary pathways for a set of stream and meteoric-derived water samples, respectively, with both groups generally being characterised as moderately alkaline, bicarbonate-dominated and Mg-rich waters. Stream water samples are supersaturated with CO2 and therefore prone to degassing, which, in combination with evaporation, drives carbonate supersaturation and precipitation. Isotopic signatures indicate soil CO2 as the main carbon source in the stream waters entering the tailings pile, whereas water emerging downstream of the tailings pile may also contain carbon from the dissolution of isotopically light bedrock magnesite in an open system with respect to soil CO2. The evolution of meteoric-derived waters on the other hand, partly occurs under CO2-limited conditions, which results from reduced CO2 ingress at depth and/or a temporal lag between fluid alkalisation and kinetically hindered uptake of CO2 into alkaline solution. A high pH, Mg-rich meteoric water absorbs atmospheric CO2 after discharging into a tunnel within the tailings pile, resulting in high DIC concentrations with atmospheric carbon isotope signature. Evaporation of the water at the discharge point in the tunnel drives precipitation of hydromagnesite (Mg5(CO3)4(OH)2·4H2O), displaying a clear atmospheric isotope signature, broadly consistent with previous estimates of carbon and oxygen isotope fractionation during precipitation of hydrated Mg-carbonate. © 2016, Elsevier B.V.
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    Etching behavior of aluminum alloy extrusions
    (SpringerLink, 2014-10-16) Zhu, HL
    The etching treatment is an important process step in influencing the surface quality of anodized aluminum alloy extrusions. The aim of etching is to produce a homogeneously matte surface. However, in the etching process, further surface imperfections can be generated on the extrusion surface due to uneven materials loss from different microstructural components. These surface imperfections formed prior to anodizing can significantly influence the surface quality of the final anodized extrusion products. In this article, various factors that influence the materials loss during alkaline etching of aluminum alloy extrusions are investigated. The influencing variables considered include etching process parameters, Fe-rich particles, Mg-Si precipitates, and extrusion profiles. This study provides a basis for improving the surface quality in industrial extrusion products by optimizing various process parameters. © 2014, The Minerals, Metals & Materials Society.
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    Temperature dependence of alkali-metal rattling dynamics in the β-pyrochlores, AOs2O6 (A = K, Rb, Cs), from MD simulation
    (IOP Science, 2014-05-16) Shoko, E; Peterson, VK; Kearley, GJ
    We investigate the temperature response of the alkali-metal rattling modes in β-pyrochlores, AOs2O6 (A = K, Rb, Cs), from the results of ab initio molecular dynamics (MD) simulations performed at 20 K, 100 K and 300 K. Our results show that the temperature response of the T1u mode is clearly different from that of the T2g mode for all three pyrochlores. In this regard, two features are of particular note for both K and Rb; (1) the T1u mode exhibits a distinctly stronger softening response with decreasing temperature compared to the T2g mode, and (2) the T1u mode becomes stronger and sharper with decreasing temperature. These two findings suggest that the T1u mode is significantly more anharmonic and sensitive to the cage dynamics than the T2g mode. Examination of the local potentials around the alkali-metal atoms reveals that K has the flattest and most anharmonic potential at all temperatures while Cs exhibits the narrowest potential. The temperature dependence of the local potentials reveals that, for K, the potential at a higher temperature is not a simple extrapolation to higher energy of that at a lower temperature. Instead, we find significant reconstruction of the potential at different temperatures. Finally, we explore the temperature response of the coupling between the alkali metals and find a complex temperature dependence which suggests that the origin of the coupling may be more complex than a pure Coulomb interaction. We also find an unexpected increase in the static disorder of the system at low temperatures for the K and Rb pyrochlores. © 2014 IOP Publishing Ltd
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    Toward a mechanism of rattler coupling in the β-pyrochlores AOs2O6 (A = K, Rb, Cs)
    (Springer Link, 2014-03-03) Shoko, E; Peterson, VK; Kearley, GJ
    We have applied ab initio molecular dynamics simulations to study metal–metal coupling on the alkali-metal sublattice in the β-pyrochlore osmates, AOs2O6 (A = K, Rb, Cs) at 300 K. We find that the dynamics of the alkali-metal atoms (rattlers) exhibit stronger rattler–rattler correlations than rattler–cage correlations, and that, at 300 K, this correlation is strongest for Cs. We show that the rattler–rattler correlations control the dominant dynamics in the rattling of these atoms. We provide preliminary evidence that the rattler correlated motion occurs primarily through two somewhat distinct vibrational modes: a high-energy mode (peak A) couples the rattlers to each other and a low-energy mode (peak B) couples the rattlers to the cage modes. Rattler–rattler correlated motion through the high-energy mode provides insight into the trend in spectral broadening from Cs to K. The spectral broadening is inversely proportional to the strength of the dynamical correlations on the alkali-metal sublattice which in turn depend on the atomic size of the rattler, decreasing from Cs to K. Thus, the broadest spectrum exhibited by the K is partly a consequence of the small size of this rattler which permits a greater range of motions involving combinations of both correlated and anti-correlated dynamics. We emphasize that the identification of the somewhat distinct roles of the high-energy (peak A) and low-energy (peak B) modes in rattler coupling reported in this work is a significant step toward a complete fundamental mechanism of rattler dynamical coupling in these osmates. We believe that such a mechanism will have profound implications for a broad class of cage compounds, including clathrates and skutterudites.© 2014, Springer Science+Business Media New York.