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Mehcanical stess relaxation of a laser penned and shot penned ni-based superalloy
No full textNickel based superalloy IN718 specimens were subjected to laser peening and shot peening. The residual stress and work hardening introduced by laser peening and shot peening were characterized using neutron diffraction method and electron backscattered diffraction (EBSD). A modified set up in reflective mode was utilized during neutron diffraction to optimize the spatial and temporal resolution to perform in-situ residual stress measurements at pre-determined cycle. Residual stress relaxation was only observed in the direction of loading while the residual stress in the transverse direction remained at a similar magnitude. Residual stress relaxation was observed to be most prominent in the first cycle of fatigue at R ratio = 0.1 with little stress relaxation in subsequent fatigue load cycles. Under tensile-tensile loading, stress relaxation occurs when the superposition of tensile residual stress and applied loading exceeds the localized yield strength of the material. Stress relaxation was found to be well correlated with the magnitude of work hardening. Residual stress relaxation as a function of depth and number of cycles were also recorded to illustrate the changes in residual stress during the cyclic loading. © 2020 Springer Nature Switzerland AG
Fabrication, Structural Characterization and Testing of a Nanostructured Tin Oxide Gas Sensor
No full textA nanostructured SnO 2 conductometric gas sensor was produced from thermally evaporated Sn clusters using a thermal oxidation process. SnO 2 clusters were simultaneously formed in an identical process on a Si 3 N 4 membrane featuring an aperture created by a focused ion beam (FIB). Clusters attached to the vertical edges of the aperture were imaged using a transmission electron microscope. The original morphology of the Sn cluster film was largely preserved after the thermal oxidation process and the thermally oxidized clusters were found to be polycrystalline and rutile in structure. NO 2 gas sensing measurements were performed with the sensor operating at various temperatures between 25degC and 290degC. At an operating temperature of 210degC, the sensor demonstrated a normalized change in resistance of 3.1 upon exposure to 510 ppb of NO 2 gas. The minimum response and recovery times for this exposure were 45 s and 30 s at an operating temperature of 265degC. The performance of the SnO 2 sensor compared favorably with previously published results. Finally, secondary ion mass spectrometry and X-ray photoelectron spectroscopy were used to establish the levels of nitrogen present in the films following exposure to NO 2 gas. © Copyright 2009 IEE
Chemical characterisation and source identification of atmospheric aerosols in the Snowy Mountains, south-eastern Australia
Get PDFCharacterisation of atmospheric aerosols is of major importance for: climate, the hydrological cycle, human health and policymaking, biogeochemical and palaeo-climatological studies. In this study, the chemical composition and source apportionment of PM2.5 (particulate matter with aerodynamic diameters less than 2.5 μm) at Yarrangobilly, in the Snowy Mountains, SE Australia are examined and quantified. A new aerosol monitoring network was deployed in June 2013 and aerosol samples collected during the period July 2013 to July 2017 were analysed for 22 trace elements and black carbon by ion beam analysis techniques. Positive matrix factorisation and back trajectory analysis and trajectory clustering methods were employed for source apportionment and to isolate source areas and air mass travel pathways, respectively. This study identified the mean atmospheric PM2.5 mass concentration for the study period was (3.3 ± 2.5) μg m−3. It is shown that automobile (44.9 ± 0.8)%, secondary sulfate (21.4 ± 0.9)%, smoke (12.3 ± 0.6)%, soil (11.3 ± 0.5)% and aged sea salt (10.1 ± 0.4)% were the five PM2.5 source types, each with its own distinctive trends. The automobile and smoke sources were ascribed to a significant local influence from the road network and bushfire and hazard reduction burns, respectively. Long-range transport are the dominant sources for secondary sulfate from coal-fired power stations, windblown soil from the inland saline regions of the Lake Eyre and Murray-Darling Basins, and aged sea salt from the Southern Ocean to the remote alpine study site. The impact of recent climate change was recognised, as elevated smoke and windblown soil events correlated with drought and El Niño periods. Finally, the overall implications including potential aerosol derived proxies for interpreting palaeo-archives are discussed. To our knowledge, this is the first long-term detailed temporal and spatial characterisation of PM2.5 aerosols for the region and provides a crucial dataset for a range of multidisciplinary research. Crown Copyright © 2018 Published by Elsevier B.V
Dye⋯TiO2 interfacial structure of dye-sensitised solar cell working electrodes buried under a solution of I−/I3− redox electrolyte
No full textDye-sensitised solar cells (DSCs) have niche prospects for electricity-generating windows that could equip buildings for energy-sustainable future cities. However, this ‘smart window’ technology is being held back by a lack of understanding in how the dye interacts with its device environment at the molecular level. A better appreciation of the dye⋯TiO2 interfacial structure of the DSC working electrodes would be particularly valuable since associated structure–function relationships could be established; these rules would provide a ‘toolkit’ for the molecular engineering of more suitable DSC dyes via rational design. Previous materials characterisation efforts have been limited to determining this interfacial structure within an environment exposed to air or situated in a solvent medium. This study is the first to reveal the structure of this buried interface within the functional device environment, and represents the first application of in situ neutron reflectometry to DSC research. By incorporating the electrolyte into the structural model of this buried interface, we reveal how lithium cations from the electrolyte constituents influence the dye⋯TiO2 binding configuration of an organic sensitiser, MK-44, via Li+ complexation to the cyanoacrylate group. This dye is the molecular congener of the high-performance MK-2 DSC dye, whose hexa-alkyl chains appear to stabilise it from Li+ complexation. Our in situ neutron reflectometry findings are built up from auxiliary structural models derived from ex situ X-ray reflectometry and corroborated via density functional theory and UV/vis absorption spectroscopy. Significant differences between the in situ and ex situ dye⋯TiO2 interfacial structures are found, highlighting the need to characterise the molecular structure of DSC working electrodes while in a fully assembled device.
© Royal Society of Chemistry 202
Mössbauer study of the temperature dependence of electron delocalization in mixed valence freudenbergite
No full textThe evolution of the electron delocalization in the ferrous subspectra in a sample of mixed valence ferrous‐ferric freudenbergite has been followed by Mössbauer spectroscopy from 6 K to 650 K. The spectral changes do not involve the ferric component, leading to the conclusion that it is due to a thermally driven delocalization of the sixth d‐electron on the ferrous ions. The phenomenon does not occur in samples of pure ferrous freudenbergite. © 1999-2020 John Wiley & Sons, Inc
History of Australian aridity: chronology in the evolution of arid landscapes
No full textAustralian climate and vegetation, known from marine and lacustrine sediments and fossils, varied dramatically throughout the Cenozoic Era, with several warm reversals superimposed on overall drying and cooling. A suite of landforms, including stony deserts, dunefields and playa lakes, formed in response to the advancing aridity but their age generally remained uncertain until fairly recently, owing to a lack of suitable dating methods. Within the last 5 years, the chronology of Late Quaternary fluctuations of lakes, dunes and dust-mantles has been established by luminescence dating methods, and mid-Pleistocene onset of playa conditions in a few closed basins has been estimated using palaeomagnetic reversal chronology. Only recently has it been shown, by cosmogenic isotope dating, that major tracts of arid landforms including the Simpson Desert dunefield, and stony deserts of the Lake Eyre Basin, were formed in early Pleistocene and late Pliocene times, respectively. These landscapes represent a stepwise response to progressive climatic drying and, speculatively, were accompanied by biological adaptations. Recent molecular DNA studies indicate that Australia's arid-adapted species evolved from mesic-adapted ancestors during the Pliocene or earlier, but whether speciation rapidly accompanied the development of stony deserts and other arid geomorphological provinces awaits further studies of arid landscape chronology.
© The Geological Society of London 201
A wetter climate in the desert of northern Sudan 9900-7600 years ago
No full textEarly Holocene semi-aquatic and freshwater gastropod shells embedded in lake silts and clays occur in shallow depressions near Wadi Mansurab, ~15 km west of the lower White Nile in presently arid north-central Sudan. Ten new AMS radiocarbon ages obtained on shells from two of the clay pans accord with the four conventional radiocarbon ages from these sites published nearly forty years ago and show that the climate was significantly wetter in this part of the SE Sahara between 9.9 ka and 7.6 ka, with a concentration of ages (11 out of 14) within the six hundred year interval 9.0-8.4 ka. These ages are similar to the ages of the Mesolithic barbed bone harpoon sites of Tagra and Shabona, east of the lower White Nile, as well as the age of a recently mapped 450 km2 lake that was fed by an overflow channel from the main Nile in presently arid northern Sudan between 9.5 ka and 7.5 ka. Our results confirm that regionally wetter conditions away from the Nile coincided with times of high Nile flow in the early Holocene. © Copyright 2000-2013 SAHAR
Isotopic and chromatographic fingerprinting of the sources of dissolved organic carbon in a shallow coastal aquifer
Get PDFThe terrestrial subsurface is the largest source of freshwater globally. The organic carbon contained within it and processes controlling its concentration remain largely unknown. The global median concentration of dissolved organic carbon (DOC) in groundwater is low compared to surface waters, suggesting significant processing in the subsurface. Yet the processes that remove this DOC in groundwater are not fully understood. The purpose of this study was to investigate the different sources and processes influencing DOC in a shallow anoxic coastal aquifer. Uniquely, this study combines liquid chromatography organic carbon detection with organic (δ13CDOC) carbon isotope geochemical analyses to fingerprint the various DOC sources that influence the concentration, carbon isotopic composition, and character with respect to distance from surface water sources, depth below surface, and inferred groundwater residence time (using 3H activities) in groundwater. It was found that the average groundwater DOC concentration was 5 times higher (5 mg L−1) than the global median concentration and that the concentration doubled with depth at our site, but the chromatographic character did not change significantly. The anoxic saturated conditions of the aquifer limited the rate of organic matter processing, leading to enhanced preservation and storage of the DOC sources from peats and palaeosols contained within the aquifer. All groundwater samples were more aromatic for their molecular weight in comparison to other lakes, rivers and surface marine samples studied. The destabilization or changes in hydrology, whether by anthropogenic or natural processes, could lead to the flux of up to 10 times more unreacted organic carbon from this coastal aquifer compared to deeper inland aquifers
Radionuclide bioaccumulation in trees at an Australian legacy low-level waste site: concentration patterns in branches and foliage
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Accelerator based ion beam analysis techniques contribute to a better understanding of long range fine particle pollution in asia
No full textFine-particle pollution in large populated Asian cities can be very high compared with internationally accepted health goals. Much of this fine-particle pollution is produced by motor vehicles, fossil-fuel combustion, industrial processes and even windblown soils from desert regions. As part of a long term project in the Asian region with support from the IAEA, ANSTO has been using nuclear techniques not only to characterize fine-particle pollution, but also to quantify their sources and origins within Vietnam. © International Atomic Energy Agenc