Browsing by Author "Wang, Z"

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    Climate and groundwater recharge: the story from Australian caves
    (National Centre for Groundwater Research And Training, 2017-07-11) Baker, AA; Treble, PC; Markowska, M; Andersen, MS; Wang, Z; Mahmud, K; Cuthbert, MO; Coleborn, K; Rau, GC
    Quantifying the timing and extent of diffuse groundwater recharge is crucial for our understanding of groundwater recharge processes. However, diffuse recharge is notably difficult to measure directly. Caves can be used as natural observatories of ongoing diffuse recharge processes, and speleothems (cave carbonate deposits such as stalagmites) as archives of past recharge. Cave records can improve our understanding of diffuse recharge in the context of climate change and past climate variability. A long-term, national monitoring program of infiltration into caves has been undertaken since 2010 using a network of over 200 automated loggers. This has been supplemented by artificial irrigation experiments at one semi-arid site. The timing of past recharge can be determined from the periods of past stalagmite growth. Recharge characteristics can be elucidated from oxygen isotope composition, with increased 18O likely caused by evaporative fractionation and increased 16O from high intensity/magnitude rainfall events. Automated logger data identify the diffuse recharge thresholds that vary with climate and geology. Both the logged data of natural events and the artificial irrigation experiments identify significant spatial heterogeneity in recharge in these karstified systems. Water infiltrating into the karst is often depleted in the lighter oxygen isotope due to soil and shallow subsurface evaporative fractionation. Speleothem deposition is more frequent during glacial periods, presumably because recharge thresholds are lower, and their isotopic composition provides evidence of the characteristics of the recharge process. Caves provide direct access into the unsaturated zone. Direct observation of groundwater recharge can be used to complement data from the saturated zone (boreholes) and models. The heterogeneity of recharge in karst aquifers can be directly observed and quantified. Speleothems preserve a record of groundwater recharge that can extend back for hundreds of thousands of years, providing a long-term view on the timing and variability of groundwater recharge in Australia.
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    Effects of heat treatment on microstructure and mechanical properties of wire arc additively manufactured Hastelloy C276 alloy
    (Materials Australian and The Australian Ceramic Society, 2022-06-01) Qiu, Z; Wu, B; Zhu, H; Wang, Z; Wexler, D; Van Duin, S; Pan, Z; Li, H
    Hastelloy C276 is a Ni-Cr-Mo based superalloy which has a high potential for application in high temperature and extreme corrosive environment due to its high corrosion resistance and excellent mechanical properties. In this research, the wire arc additive manufacturing (WAAM) process was successfully used to fabricate the defect-free Hastelloy C276 component. The microstructure of the component was characterized using optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction, the mechanical properties were evaluated via tensile and hardness tests. The as-deposited component exhibited anisotropy on both microstructure and mechanical properties. The influences of solid solution heat treatment and stress relief heat treatment on microstructure and mechanical properties were also investigated. It was found that both microstructure and mechanical properties were significantly modified after heat treatment. Preliminary creep tests indicted the texture has a strong influence on the creep performance of the component.
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    Hydride precipitation and its influence on mechanical properties of notched and unnotched Zircaloy-4 plates
    (Elevier Science BV., 2013-05-01) Wang, Z; Garbe, U; Li, HJ; Harrison, RP; Toppler, K; Studer, AJ; Palmer, T; Planchenault, G
    The hydride formation and its influence on the mechanical performance of hydrided Zircaloy-4 plates containing different hydrogen contents were studied at room temperature. For the unnotched plate samples with the hydrogen contents ranging from 25 to 850 wt. ppm, the hydrides exerted an insignificant effect on the tensile strength, while the ductility was severely degraded with increasing hydrogen content. The fracture mode and degree of embrittlement were strongly related to the hydrogen content. When the hydrogen content reached a level of 850 wt. ppm, the plate exhibited negligible ductility, resulting in almost completely brittle behavior. For the hydrided notched plate, the tensile stress concentration associated with the notch tip facilitated the hydride accumulation at the region near the notch tip and the premature crack propagation through the hydride fracture during hydriding. The final brittle through-thickness failure for this notched sample was mainly attributed to the formation of a continuous hydride network on the thickness section and the obtained very high hydrogen concentration (estimated to be 1965 wt. ppm). © 2013, Elsevier Ltd.
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    Hydrogen-induced microstructure, texture and mechanical property evolutions in a high-pressure torsion processed zirconium alloy
    (Elsevier Ltd., 2012-11-01) Wang, Z; Garbe, U; Li, HJ; Studer, AJ; Harrison, RP; Callaghan, MD; Wang, Y; Liao, XZ
    The gaseous hydriding-induced evolutions of the microstructure, texture and mechanical properties of Zircaloy-4 processed by high-pressure torsion (HPT) were assessed. Much delta-ZrH(1.66) precipitation at 15 atm (21%) incurred significant hardening of vacuum-annealed HPT samples, and pure epsilon-ZrH(2) obtained at 20 atm showed a superior microhardness of 470 HV(0.3) and a low fracture toughness of 0.63 MPa m(1/2). The delta-hydrides presented strong (1 1 1) texture and followed the (0 0 0 1)(alpha-Zr)//{1 1 1}(delta-ZrH1.66) orientation relationship with the alpha-Zr matrix. During hydriding, alpha-Zr recrystallization texture was developed from the initial deformation texture. Copyright © 2012 Acta Materialia Inc.
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    Neutron scattering unravels the structure of tunable fibrin networks
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Wang, Z; Lauko, J; Kijas, A; Gilbert, EP; Mata, JP; Turunen, P; Rowan, AE
    Three-dimensional (3D) in vitro cell culture in natural hydrogels has shown promising results in tissue engineering and biophysics as it mimics the native extracellular matrix [1]. However, compared to biosynthetic materials, the often uncontrollable and unstable structural and mechanical properties of natural hydrogels have hindered their wide use. Fibrin is a natural fibrous material that has drawn much interest in tissue engineering and has been employed as a scaffold for 3D cell culture because of its inherent advantages. Yet, the batch-to-batch variation, rapid degradation, uncontrollable structural and mechanical properties are the main shortcomings [2]. To overcome these shortcomings, we have established a new well-defined fibrin network with tuneable architecture and mechanical properties by employing two potent recombinant snake venom proteins. Firstly, a Procoagulant Snake Venom Protein (PSVP), which rapidly activates the thrombin precursor prothrombin, is employed for fibrin network formation; a second recombinant snake venom protein, Anti-fibrinolytic Snake Venom Protein (ASVP) is also utilized to control the fibrin degradation. Initially, confocal laser scanning fluorescence microscopy (CLSM) was employed to characterize the micro-scale structural properties. However, while CLSM can provide detailed information about the network structure, the optical resolution of CLSM is not sufficient to visualize the internal structure of individual fibers. Moreover, the fluorophores that are required for the detection can potentially interfere with the fibrin polymerization. Therefore, we utilised combined small angle neutron scattering (SANS) and ultra-small angle neutron scattering (USANS) techniques to characterize and verify our new defined fibrin network system including internal structure of the individual fibres and the structure of the fibrin networks [3]. The combined SANS and USANS data of fibrin networks revealed details of the hierarchical structure at multiple length scales associated with the network, fibres and internal proto-fibrils, previously not accessible by CLSM, especially in the case of internal fibre structure. This data is key for correlating the network struc ture and the mechanical properties, which are fundamental for cellular responses including cell proliferation, migration and differentiation. © The Authors.
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    Observations of temperature stability of γ-zirconium hydride by high-resolution neutron powder diffraction
    (Elsevier, 2016-03-15) Wang, Z; Steuwer, A; Liu, N; Maimaitiyili, T; Avdeev, M; Blomqvist, J; Bjerkén, C; Curfs, C; Kimpton, JA; Daniels, JE
    The phase evolution in a zirconium–50 deuterium (Zr–50D, at.%) alloy system during thermal cycling has been investigated using in situ high-resolution neutron powder diffraction. The results showed that the peritectoid reaction α-Zr + δ-ZrD → γ-ZrD previously suggested to occur at high temperatures does not take place in the system. Slow cooling, from high temperatures (≥520 K) to room temperature at a rate of 5 K min−1, promoted the γ-hydride formation rather than fast cooling as reported earlier. In contrast to the observation that the δ-hydride present in the system remained at temperatures up to 740 K, the produced γ phase transformed to δ-hydride in the temperature range of 370 K–559 K, with the transformation completing at approximately 559 K. It is confirmed that the formation of the γ-hydride was reproducible with slow cooling, and a diffusion-controlled sluggish δ-to γ-hydride transformation is suggested to be responsible for the favorable development of γ-hydride during slow cooling. © 2015 Elsevier B.V.
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    Observations on the zirconium hydride precipitation and distribution in zircaloy-4
    (Springer Link, 2014-05-14) Wang, Z; Garbe, U; Li, HJ; Harrison, RP; Kaestner, A; Lehmann, EH
    Hydride precipitation and distribution in hot-rolled and annealed Zircaloy-4 plate samples artificially induced by gaseous hydrogen charging were studied primarily by neutron tomography, scanning electron microscopy (SEM), and SEM-based electron backscattered diffraction techniques. The precipitated hydride platelet (d-ZrH1.66) at a hydrogen pressure of 20 atm was found following the {111}d-ZrH1.66//(0001)a-Zr with the surrounding a-Zr matrix. The microstructural characterization indicated that hydrides with a relatively uniform distribution were precipitated on the rolling-transverse section of the plate, whereas, on the normal-transverse section, a hydride concentration gradient was present with a dense hydride layer near the surface. Further, the neutron tomography investigations clearly identified the nonuniform spatial distribution of hydrides. Thin hydride layers preferentially formed on the sample surface, and the concentrated hydrides precipitating at the edges/corner of the sample were observed. The causes for the localized hydride accumulation werealso discussed. © 2014, The Minerals, Metals & Materials Society and ASM International 2013.
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    Simple synchronous dual-modification strategy with Zr4+ doping and CeO2 nanowelding to stabilize layered Ni-rich cathode materials
    (American Chemical Society, 2023-05-22) Liu, JK; Yin, ZW; Zheng, WC; Zhang, J; Deng, SS; Wang, Z; Deng, Li; Xie, SJ; Liu, ZK; Avdeev, M; Qu, F; Kan, WH; Zhou, Y; Li, JT
    A Ni-rich layered oxide, one promising cathode for lithium-ion batteries (LIBs), exhibits the advantages of low cost and high capacity but suffers from rapid capacity loss due to bulk structural instability and surface side reactions. Herein, a simple synchronous dual-modification strategy with Zr4+doping and CeO2nanowelding is proposed to address such issues. Utilizing the migration energy difference of Zr and Ce ions in layered structures, one-step high-temperature sintering of LiNi0.8Co0.1Mn0.1O2particles with Zr and Ce nitrate distributions enables simultaneous doping of Zr ions in the bulk and CeO2surface modification. Therein, Zr ions in the bulk occupying the Li sites can improve the Li+diffusion rate and stabilize the crystal structure, while CeO2on the surface provides nanowelding between the grain boundaries and resistance to electrolyte erosion. Theoretical calculations and a series of structure/composition characterizations (i.e., neutron scattering, in situ X-ray diffraction, etc.) validated the proposed strategy and its role in stabilizing the Ni-rich cathodes. The synergistic effect of Zr4+doping and CeO2nanowelding enables an impressive initial capacity of 187.2 mAh g-1(2.7-4.3 V vs Li/Li+) with 86.1% retention after 200 cycles at 1 C and rate capabilities of 146.6 and 127.3 mAh g-1at 5 and 10 C, respectively. Upon increasing the testing temperature to 60 °C, the dual-modified Ni-rich cathode exhibits an initial discharge capacity of 203.5 mAh g-1with a good retention of 80.8% after 100 cycles at 0.5 C. The present strategy utilizing the migration energy difference of metal ions to achieve synchronous bulk doping and surface modification will offer fresh insights to stabilize layered cathode materials for LIBs, which can be widely used in other kinds of batteries with various cathode materials. © American Chemical Society