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Evaluation of the residual stress in the cold spray technique using smooth particle hydrodynamics modelling and neutron diffraction
No full textCold spray is a material deposition technique in which powdered metals are deposited onto metallic and glass substrates as a means of improving functionality, repair or protection of the underlying substrate. The residual stress that builds up in the material during spraying is closely linked to the coating’s integrity and the bonding mechanism. Neutron diffraction residual stresses measurements were carried out at the OPAL research reactor, ANSTO, using the KOWARI strain scanner to investigate an Al-6061 sample with a fine through-thickness resolution of 0.5 mm. The experimentally determined through thickness stress profiles of the macroscopically thick coatings were used to validate FE calculations made for 100 μm thick coatings using the Smooth Particle Hydrodynamics, SPH, techniques. A pronounced plastic strain gradient was apparent in the tested and modelled samples indicative of the significant residual macro-stresses which develop in the cladding/substrate during the deposition. Around the deposited particle’s periphery (in the jetting region) the temperatures are significant, this lends itself to the presence of grain refinement at the periphery of sprayed particles and the propagation of dynamic recrystallization which is closely coupled with the thermal softening of the particle. © 2014, Trans Tech Publications
Metal speciation and potential bioavailability changes during discharge and neutralisation of acidic drainage water
No full textThe discharge of acid drainage from the farm irrigation areas to the Murray River in South Australia represents a potential risk to water quality. The drainage waters have low pH (2.9–5.7), high acidity (up to 1190 mg L−1 CaCO3), high dissolved organic carbon (10–40 mg L−1), and high dissolved Al, Co, Ni and Zn (up to 55, 1.25, 1.30 and 1.10 mg L−1, respectively) that represent the greatest concern relative to water quality guidelines (WQGs). To provide information on bioavailability, changes in metal speciation were assessed during mixing experiments using filtration (colloidal metals) and Chelex-lability (free metal ions and weak inorganic metal complexes) methods. Following mixing of drainage and river water, much of the dissolved aluminium and iron precipitated. The concentrations of other metals generally decreased conservatively in proportion to the dilution initially, but longer mixing periods caused increased precipitation or adsorption to particulate phases. Dissolved Co, Mn and Zn were typically 95–100% present in Chelex-labile forms, whereas 40–70% of the dissolved nickel was Chelex-labile and the remaining non-labile fraction of dissolved nickel was associated with fine colloids or complexed by organic ligands that increased with time. Despite the different kinetics of precipitation, adsorption and complexation reactions, the dissolved metal concentrations were generally highly correlated for the pooled data sets, indicating that the major factors controlling the concentrations were similar for each metal (pH, dilution, and time following mixing). For dilutions of the drainage waters of less than 1% with Murray River water, none of the metals should exceed the WQGs. However, the high concentrations of metals associated with fine precipitates within the receiving waters may represent a risk to some aquatic organisms. © 2013, Elsevier Ltd
Iron deposition in modern and archaeological teeth
No full textIron surface concentrations and profile maps were measured on the enamel of archaeological and modern teeth to determine how iron is deposited in tooth enamel and if it was affected by the post-mortem environment. Teeth from Australian children who died in the second half of the 19th century were compared with contemporary teeth extracted for orthodontic purposes. Surface analysis of the teeth was performed using the 3 MV Van Der Graff Accelerator at The Australian Nuclear Science and Technology Organisation (ANSTO), Sydney, Australia. A small sample of teeth were then cut in the mid sagittal plane and analysed using ANSTO High Energy Heavy Ion Microprobe. Maps and linear profiles were produced showing the distribution of iron across the enamel. Results show that both the levels and distribution of iron in archaeological teeth is quite different to contemporary teeth, raising the suggestion that iron has been significantly altered by the post-mortem environment
Pressure-induced intersite Bi[BOND]M (M=Ru, Ir) valence transitions in hexagonal perovskites
No full textPressure-induced charge transfer from Bi to Ir/Ru is observed in the hexagonal perovskites Ba3+nBiM2+nO9+3n (n=0,1; M=Ir,Ru). These compounds show first-order, circa 1 % volume contractions at room temperature above 5 GPa, which are due to the large reduction in the effective ionic radius of Bi when the 6s shell is emptied on oxidation, compared to the relatively negligible effect of reduction on the radii of Ir or Ru. They are the first such transitions involving 4d and 5d compounds, and they double the total number of cases known. Ab initio calculations suggest that magnetic interactions through very short (ca. 2.6 Å) M[BOND]M bonds contribute to the finely balanced nature of their electronic states. © 2014 WILEY‐VCH
Tuning the giant magnetoelastic transition in Ba3BiIr2O9 and Ba3BiRu2O9
No full textWe have experimentally investigated the effects of pressure on the magnetoelastic transitions associated with the opening of spin-gaps in Ba3BiIr2O9 and Ba3BiRu2O9. For both compounds,
reducing the unit cell volume by either external physical and internal chemical pressure was
found to reduce the temperature T*
of the transition and, to a lesser extent, the magnitude of
the associated negative thermal volume expansion. The results yield the latent heat associated
with the transitions, −3.34(3) × 102
J mol−1 for Ba3BiIr2O9 and −7.1(5) × 102
J mol−1 for
Ba3BiRu2O9. The transition in Ba3BiRu2O9 is significantly more robust than in Ba3BiIr2O9,
requiring an order of magnitude higher pressures to achieve the same reduction in T*
. The
differing responses of the two compounds points to differences between the 4d and 5d metals and hence to the importance of spin-orbit coupling, which is expected to be much stronger in the Ir compound.© 2014,IOP Publishing Ltd
Identifying flood recharge and inter-aquifer connectivity using multiple isotopes in subtropical Australia
Get PDFAn understanding of hydrological processes is vital for the sustainable management of groundwater resources, especially in areas where an aquifer interacts with surface water systems or where aquifer interconnectivity occurs. This is particularly important in areas that are subjected to frequent drought/flood cycles, such as the Cressbrook Creek catchment in Southeast Queensland, Australia. In order to understand the hydrological response to flooding and to identify inter-aquifer connectivity, multiple isotopes (δ2H, δ18O, 87Sr/86Sr, 3H and 14C) were used in this study in conjunction with a comprehensive hydrochemical assessment, based on data collected 6 months after severe flooding in 2011. The relatively depleted stable isotope signatures of the flood-generating rainfall (δ2H: −30.2 to −27.8‰, δ18O: −5.34 to −5.13‰ VSMOW) were evident in surface water samples (δ2H: −25.2 to −23.2‰, δ18O: −3.9 to −3.6‰ VSMOW), indicating that these extreme events were a major source of recharge to the dam in the catchment headwaters. Furthermore, stable isotopes confirmed that the flood generated significant recharge to the alluvium in the lower part of the catchment, particularly in areas where interactions between surface waters and groundwater were identified and where diffuse aquifer recharge is normally limited by a thick (approximately 10 m) and relatively impermeable unsaturated zone. However, in the upper parts of the catchment where recharge generally occurs more rapidly due to the dominance of coarse-grained sediments in the unsaturated zone, the stable isotope signature of groundwater resembles the longer-term average rainfall values (δ2H: −12.6, δ18O: −3.4‰ VSMOW), highlighting that recharge was sourced from smaller rainfall events that occurred subsequent to the flooding. Interactions between the bedrock aquifers and the alluvium were identified at several sites in the lower part of the catchment based on 87Sr/86Sr ratios; this was also supported by the hydrochemical assessment, which included the modelling of evaporation trends and saturation indices. The integrated approach used in this study facilitated the identification of hydrological processes over different spatial and temporal scales, and the method can be applied to other complex geological settings with variable climatic conditions.© 2015, Author(s)
Initial assessment of an empirical potential as a portable tool for rapid investigation of Li+ Diffusion in Li+-Battery cathode materials
No full textSubstantial research activity is currently invested in the pursuit of next
generation cathode materials for rechargeable Li-ion batteries. We carry out an initial
assessment of the suitability of a recently described empirical potential [J. Phys. Chem. B
2006, 110, 11780] as a rapid, portable, and at least qualitatively accurate computational
tool for screening large numbers of potential cathode materials for favorable Li-ion
transport capabilities. Selected materials can then be examined more elaborately with more
accurate but computationally more expensive first-principles approaches. As test systems
for our initial assessment, we chose the group of phosphate olivines LiMPO4 (M = Mn, Fe,
Co, Ni), promising candidates for next generation cathode materials and subject of
numerous experimental and computational studies. To conduct the assessment, we
determined the ground state structures of LiMPO4 from geometry optimizations with this
empirical potential and with density functional theory (DFT) and computed activation
barriers of Li-ion diffusion in LiMPO4 from molecular dynamics simulations based on the
empirical potential and from minimum-energy-path DFT calculations. We show that structural results generated by the empirical
potential are in good agreement with the DFT and experimental results and that barrier results produced by this potential are in
good agreement with the DFT results and often in better agreement than values generated by custom parametrized empirical
potentials. © 2014, American Chemical Society
Strategies to control the spectral properties of Au–Ni thin films
No full textGold and nickel have quite different dielectric functions. Here we use a combination of calculation and sample manufacture to assess two strategies by which thin films of these elements can be produced with a controlled range of far-field optical properties. In the first approach, control can be achieved by manipulating the density of states of metastable solid solutions, which in turn controls the dielectric function. In the second approach the optical properties of the films are controlled by varying the geometry of stacks fabricated from the constituent elements. We show that the two approaches can produce equivalent results so both are viable options in practice. Modeling is used to reveal how the structure controls the optical properties and to map out the possible color gamut. Predictions are tested with thin film samples fabricated by magnetron sputtering. © 2013, Elsevier B.V
Host–guest adsorption behavior of deuterated methane and molecular oxygen in a porous rare-earth metal–organic framework
No full textThe yttrium-based metal–organic framework, Y(btc) (btc = 1,3,5-benzenetricarboxylate), shows moderate uptake of methane (0.623 mmol g−1) and molecular oxygen (0.183 mmol g−1) at 1 bar and 308 K. Neutron powder-diffraction data for the guest-free, CD4-, and O2-loaded framework reveal multiple adsorption sites for each gas. Both molecular guests exhibit interactions with the host framework characterised by distances between the framework and guest atoms that range from 2.83 to 4.81 Å, with these distances identifying interaction most commonly between the guest molecule and the carboxylate functional groups of the benzenetricarboxylate bridging ligand of the host. © 2014, International Centre for Diffraction Data
Sulfate isotope compositions (δ34S, δ18O) and strontium isotopic ratios (87Sr/86Sr) of Triassic evaporites in the Betic Cordillera (SE Spain)
No full textSulfate isotope compositions (δ34S and δ18O) and strontium isotope ratios (87Sr/86Sr) of Triassic evaporites in the Betic Cordillera are addressed for the first time in the present work. Isotope values
have been determined in gypsum and anhydrite samples of the Germanic-type facies (Buntsandstein,
Muschelkalk and Keuper) coming from different outcrops spanning the complete Triassic Period and corresponding
to both the Internal Zones and the External (Prebetic, Subbetic) Zones of this chain. More precise age assignments and stratigraphic controls are often obscured because of the intense halokinetic
and tectonic deformation occurred during the Alpine Orogeny in the Betic Cordillera. Isotope values of Triassic sulfates obtained in the present study range between 12.5 and 16.6 ‰ for δ34S, between 8.9 and
16.9 ‰ for δ18O, and between 0.707615 and 0.708114 for 87Sr/86Sr. These values, as a whole, are in agreement with those of worldwide Triassic marine evaporites