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Time series of tritium, stable isotopes and chloride reveal short-term
No full textA major limitation to the assessment of catchment transit time (TT) stems from the use of stable isotopes or chloride as hydrological tracers, because these tracers are blind to older contributions. Yet, accurately capturing the TT of the old water fraction is essential, as is the assessment of its temporal variations under non-stationary catchment dynamics.
In this study we used lumped convolution models to examine time series of tritium, stable isotopes and chloride in rainfall, streamwater and groundwater of a catchment
located in subtropical Australia. Our objectives were to determine the different contributions to streamflow and their variations over time, and to understand the relationship between catchment TT and groundwater residence time. Stable
isotopes and chloride provided consistent estimates of TT in the upstream part of the catchment. A young component to streamflow was identified that was partitioned into quickflow (mean TT 2 weeks) and discharge from the fractured igneous rocks forming the headwaters (mean TT 0.3 years).
The use of tritium was beneficial for determining an older contribution to streamflow in the downstream area. The best
fits between measured and modelled tritium activities were obtained for a mean TT of 16–25 years for this older groundwater
component. This was significantly lower than the residence time calculated for groundwater in the alluvial aquifer feeding the stream downstream ( 76–102 years), emphasising the fact that water exiting the catchment and water stored in it had distinctive age distributions. When simulations were run separately on each tritium streamwater sample, the TT of
old water fraction varied substantially over time, with values averaging 17 6 years at low flow and 38 15 years after
major recharge events. This counterintuitive result was interpreted as the flushing out of deeper, older waters shortly after
recharge by the resulting pressure wave propagation. Overall, this study shows the usefulness of collecting tritium data in
streamwater to document short-term variations in the older component of the TT distribution. Our results also shed light
on the complex relationships between stored water and water in transit, which are highly non-linear and remain poorly understood. © 2016, Author(s)
Stress distribution in iron powder during die compaction
No full textThe unique and unusual state of matter represented by granular materials has historically made it very difficult to develop models of stress distributions and was previously not able to be explored experimentally in the required detail. This paper reports the application of the neutron diffraction strain scanning method, originally developed for residual stress measurements within engineering components, to the problem of the stress distribution in granular Fe under a consolidating pressure. Strains were measured in axial, radial, circumferential and an oblique direction using the neutron strain scanning diffractometer KOWARI at ANSTO (Sydney). The full stress tensor as a function of position was able to be extracted for both straight walled, converging and stepped dies. © 2014, Trans Tech Publications
Physical thermo-mechanical simulation of magnesium: An in-situ diffraction study
No full textTime-resolved, two-dimensional synchrotron high-energy X-ray diffraction has been utilized for the in-situ investigation of the microstructural evolution of magnesium, during heating and during plastic deformation at various temperatures. Throughout static heating of the as-extruded material, first recovery, then recrystallization and finally grain growth occurred with increasing temperature. Grain rotation was observed during grain growth of the static heated samples. Subsequent plastic deformation, through compression, at lower temperatures revealed the activated deformation systems. At room temperature, extension-twinning flips the crystallite orientations abruptly from the extrusion to the compression fiber texture. In contrast, at elevated temperatures, twinning is negligible and the texture reorientation progresses in a gradual steady-state flow regime, ending in a tilted basal texture with a tilt angle depending on the degree of deformation. The methodology described herein offers parametric studies related to microstructural and deformation processes in an unprecedented way. © 2014, Published by Elsevier B.V
Temperature induced internal stress in carrara marble
No full textStone physical weathering, deterioration and damage (e.g. bowing, cracking, microfracturing) represent a serious problem for preservation of sculptural and architectural heritage objects. Although different mechanisms of such degradation might be responsible (e.g. chemical or biogenic), there is an understanding in the geological community that physical reasons for stone degradation and role of stress are of primary importance. In this work Carrara marble was a chosen for investigation: a calcitic type with ~20% of dolomite. Neutron diffraction was used to investigate the phase composition, the texture, and the strain/stress in calcite and dolomite phases in a bulk marble sample. Evolution of the stress state was studied by measuring strains in calcite and dolomite at two temperatures with clear evidence of thermally induced microstresses. Results are discussed in connection to the theory of composite materials and a micro-mechanical explanation of the general problem of marble deterioration is suggested. © 2014, Trans Tech Publications
Peroxide defect formation in zirconate perovskites
No full textAtomic scale modelling suggests that excess oxygen can be accommodated in the group II perovskite zirconates by the formation of peroxide ion defects. This is unprecedented given the lack of charge compensating defects required for standard excess oxygen accommodation. The solution energy of O2 was predicted to be close to zero for BaZrO3, accommodating the peroxide ion defect more easily than in SrZrO3 or CaZrO3. This was experimentally examined by exposing SrZrO3 and BaZrO3 to hydrogen peroxide solution and then carrying out Raman spectroscopy measurements to look for a peak indicative of peroxide ions. A peak was observed at ∼1000 cm−1 in both compositions, suggesting the theoretically predicted peroxide ion is present. © 2014, The Royal Society of Chemistry
Synthetic, structural, and electrochemical study of Monoclinic Na4Ti5O12 as a sodium-ion battery anode material
No full textThe monoclinic phase of Na4Ti5O12 (M-Na4Ti5O12) has been investigated as a potential sodium-ion battery anode material. In contrast to the previously investigated trigonal phase (T-Na4Ti5O12), M-Na4Ti5O12 has continuous two-dimensional (2D) channels with partially occupied Na sites, providing broader pathways and more space for the intercalation of excess sodium. Electrochemical measurements show that it exhibits a comparable or higher reversible capacity than T-Na4Ti5O12. Neutron powder diffraction reveals the preferred sites and occupancies of the excess sodium. In situ synchrotron X-ray diffraction under electrochemical cycling shows that the crystal lattice undergoes strongly anisotropic volume changes during cycling. © 2014, American Chemical Society
Neutron diffraction residual stress measurements of welds made with pulsed tandem gas metal arc welding (PT-GMAW)
No full textPulsed tandem gas metal arc welding (PT-GMAW) is being developed to increase productivity and minimise weld-induced distortion in ship-building. The PT-GMAW process was used in pulse–pulse mode to butt-weld two different strength and thickness steels; the residual stress and hardness profiles of the welds are reported and correlated
Characterization of the seposition of n-Octanohydroxamate on copper surfaces
No full textThe interaction of n-octanohydroxamate with a copper electrode was investigated using cyclic voltammetry, contact angles, surface-enhanced Raman scattering, neutron reflectometry and X-ray reflectometry. The data demonstrated that hydroxamate specifically adsorbed at underpotentials in the keto tautomeric form, but the layer was hydrophilic and contained >50% water. In the CuI stability region the hydroxamate moiety took on the enol tautomeric form but the interface remained hydrated. Co-adsorption of electrolyte species was observed at underpotentials. The adsorbed hydroxamate at the surface did not prevent the formation of oxide in the CuI stability region. A hydrophobic non-passivating multilayer of copper n-octanohydroximate formed in the CuII stability region. © 2014, The Electrochemical Society
The early rise and late demise of New Zealand’s last glacial maximum
No full textRecent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (∼30–20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28–16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26–19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19–16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28–20 ka, and gradual deglaciation until at least 15 ka. © 2014, National Academy of Sciences of the United States of America
Dripwater organic matter and trace element geochemistry in a semi-arid karst environment: Implications for speleothem paleoclimatology
No full textA series of four short-term infiltration experiments which revealed hydrochemical responses relevant to semi-arid karst environments were carried out above Cathedral Cave, Wellington, New South Wales (NSW), Australia. Dripwater samples were collected at two sites for trace element and organic matter analysis. Organic matter was characterised using fluorescence and interpreted using a PARAFAC model. Three components were isolated that represented unprocessed, soil-derived humic-like and fulvic-like material, processed humic/fulvic-like material and tryptophan-like fluorescence. Principal Component Analysis (PCA) performed on the entire dataset comprising trace element concentrations and PARAFAC scores revealed two dominant components that were identified as soil and limestone bedrock. The soil component was assigned based on significant contributions from the PARAFAC scores and additionally included Ba, Cu, Ni and Mg. The bedrock component included the expected elements of Ca, Mg and Sr as well as Si. The same elemental behaviour was observed in recent stalagmite growth collected from the site. Our experiments demonstrate that existing paleoclimate interpretations of speleothem Mg and Sr, developed in regions of positive water balance, are not readily applicable to water limited environments. We provide a new interpretation of trace element signatures unique to speleothems from water limited karst environments. © 2014, Elsevier Ltd