Browsing by Author "Clark, SM"
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- ItemDetermination of the elastic properties of amorphous materials: case study of alkali-silica reaction gel(Elsevier, 2013-12-01) Moon, J; Speziale, S; Meral, C; Kalkan, B; Clark, SM; Monteiro, PJMThe gel formed during Brillouin spectroscopy reaction (ASR) can lead to cracking and deterioration of a concrete structure. The elastic properties of the ASR gel using X-ray absorption and Brillouin spectroscopy measurements are reported. X-ray absorption was used to determine the density of the gel as a function of pressure, and the result yields an isothermal bulk modulus of 33 ± 2 GPa. Brillouin spectroscopy was applied to measure isentropic bulk (24.9–34.0 GPa) and shear moduli (8.7–10.1 GPa) of the gel. The range of values obtained is attributed to the variable composition of samples that were collected under field conditions. Results suggested that amorphous silica becomes expanded and compressible as it absorbs water molecules and alkali ions. This could explain high gel migration rates through the complex pore structures in concrete. © 2013, Elsevier Ltd.
- ItemFew-layer graphene under high pressure: raman and x-ray diffraction studies(Elsevier, 2013-01-01) Clark, SM; Jeon, KJ; Chen, JY; Yoo, CSThe effect of pressure on the structure of few-layer graphene has been investigated to 50 GPa in both quasi-hydrostatic and non-hydrostatic conditions, using X-ray diffraction and Raman spectroscopy. The results indicate that few-layer graphene loses its long-range order at the critical interlayer distance of ∼2.8 Å (or above ∼18 GPa), while maintaining the local sp2 hybridization in the layer to 50 GPa. This suggests that graphene not only has the highest stability of all graphitic layer structures, but also becomes one of the most healable structures under large stress. © 2012, Elsevier Ltd.
- ItemHow to take a perfect image with DINGO(Australian Nuclear Science and Technology Organisation, 2021-11-24) Grigorova, V; Clark, SM; Bevitt, JJNeutron tomography is a powerful non-destructive technique used to study the internal structure of opaque objects. Neutron images are obtained by exposing an object to a uniform neutron beam. The transmitted neutrons interact with a phosphor which converts from neutrons to visible light, which is then demagnified on to a CCD camera. The modulation transfer function (MTF) is routinely used to determine the sharpness of an image, i.e. the ability of the imaging system to transfer information from an object to an image. The spatial frequency (SF) is the rate of transition between light and dark features in the image. For a perfect system where all of the frequency information is passed from object to image equally, the MTF of the will be 1 or 100% for all spatial frequencies and all features and contrast in the object will be transferred to the image. We performed a series of measurements to optimise the time necessary to obtain high-resolution radiographs with the DINGO instrument. We determined the MTF over a range of experimental conditions to understand the various contributions of DINGO’s imaging system variables to radiograph resolution. The system components varied in this study are the two beam modes, different scintillator screens, and pixel resolution of different cameras and lenses. We also compared the different exposure times of the object to the neutron beam to try to understand the minimum exposure time that will generate good resolution radiographs. Details of the use of this method for determining the quality of a neutron tomographic imaging system will be presented and the MTF data will be used to determine the optimal operating arrangement. © 2021 The Authors
- ItemMigration and formation of an iron rich layer during acidic corrosion of concrete with no steel reinforcement(Elsevier, 2021-11-22) Taheri, S; Giri, P; Ams, M; Bevitt, JJ; Bustamante, H; Madadi, M; Kuen, T; Gonzalez, J; Vorreiter, L; Withford, M; Clark, SMThe present study aimed to study the formation, enrichment, and relocation of iron-rich regions in the corroded area of concrete blocks, made without rebar, subjected to severely corrosive highly acidic conditions. In this work, three different concrete mix designs (a proprietary ready-mixed concrete, and laboratory made mortar and concrete) were corroded under induced accelerated conditions in sulfuric acid solutions at pH 1 for a duration of one to six months, in the absence of reinforcement (i.e. rebar) or iron-oxidizing bacteria. A variety of physicochemical and mechanical techniques were applied to monitor and assess the corrosion progress, and physical and chemical changes in the corroded samples. Results indicated a pronounced presence of iron rich layer (iron oxide/hydroxide) at the border of the corrosion front and the transition zone in all mix designs in the form of a ring. While existing papers in the literature describe the iron coming from the rebar, the only source of mobile iron in this experiment was from the iron oxide (Fe2O3) already in the cement. This zone (in a form of a ring) had an average iron content of 2.0 wt% and moved away from the surface to the center of the samples submerged in a sulfuric acid bath with the increase of immersion time, and it was accompanied by hairline cracks. The movement of this zone was in the same direction as sulfate (from acidic media) ingress and the opposite direction of calcium ion leaching, (Ca leaching). The rate of corrosion, the hardness and the compressive strength of concrete are mostly affected by the concrete mix design, the iron-ring enrichment and relocation had no significant impact on them. Detection of the iron-rich zone is an indication of the depth of corrosion at advanced stages in concrete products. © 2021 Elsevier Ltd
- ItemNeutron imaging for calculating hydrogen diffusivity in polycrystalline forsterite aggregates(American Geophysical Union, 2018-12-13) Patabendigedara, SK; Clark, SM; Salvemini, FAn understanding of hydrogen diffusion in nominally anhydrous minerals is essential for the correct interpretation of conductivity dissimilarity in the Earth mantle. The mechanism of hydrogen diffusion in dominant mantle minerals was described by Demouchy (2010) using a defect model in crystalline materials. The effects of in-grain and grain boundary diffusion are separated using the bricklayer model and other derivatives of it (Tuller 2000). Separation of the two components of proton conductivity in olivine will substantially improve the current proton conduction model. It will help to interpret magnetotelluric data and will give prospects to find new mineral sources and explain other phenomena such as volcanism and plate tectonics. A recent insight is that the high conductivities determined from proton conduction measurements at low temperatures are mainly due to conduction along grain boundaries (Demouchy 2010). We have repeated Demouchy (2010) experiment using neutron imaging to image time and temperature dependent hydrogen diffusion profiles as neutrons are highly sensitive to hydrogen. We carried out a series of experiments where we diffused H2O through a forsterite polycrystalline matrix at high-pressure and temperature. The recovered samples were imaged using the DINGO neutron tomography facility at the Australian Centre for Neutron Scattering. The results indicate hydrogen transport inside the forsterite aggregates as changing neutron attenuation along the diffusion direction of the polycrystalline mineral block. It correlates with the temperature dependent hydrogen diffusion in this mineral. This study revealed the ability of neutron imaging technique to find the hydrogen diffusion coefficient of forsterite. We are sharing these results in this conference.
- ItemOptimisation of a neutron imaging system using the modulation transfer function(Elsevier, 2023-12) Grigorova, V; Giri, P; Bevitt, JJ; Clark, SMThe use of the modulation transfer function was explored for the characterisation and optimisation of the optical system used for tomographic imaging on the DINGO instrument at the Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Lucas Heights, Australia. Both a Siemens star and a phantom were used to determine the modulation transfer function and the results are compared. This allowed the optimal configuration of the instrument to be determined and the establishment of a relationship between sample dimension, exposure time and radiograph resolution to be developed. For tomographic studies of large samples, best results were achieved with DINGO configured in high-flux mode (L/D = 500), with a 6LiF/ZnS scintillator screen, an Iris 15TM sCMOS detector, a 50 mm lens, and an exposure time between 4 and 8 s. © 2023 The Authors. Published by Elsevier B.V. - Open Access CC-BY.
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- ItemPressure-induced polyamorphism and formation of 'aragonitic' amorphous calcium carbonate(John Wiley and Sons, 2013-07-01) Fernandez-Martinez, A; Kalkan, B; Clark, SM; Waychunas, GAAmorphous calcium carbonate (ACC) is a precursor to the crystalline phases of CaCO3, commonly found in the earliest stages of biomineral development and as one of the metastable states formed during the inorganic precipitation of calcium carbonate crystalline polymorphs.1 Its isotropic and hydrous moldable character allows many organisms to form very complex conformations of their shells or skeletons by taking advantage of these unique properties.2 At least two different phases of biogenic ACC have been described to date: a highly hydrated phase with one water molecule per CaCO3 unit, and an anhydrous phase that forms as a transient phase prior to crystallization to vaterite or calcite. Recently, the existence of polyamorphism (the existence of a substance in different amorphous modifications, akin to polymorphism in crystalline materials) in synthetic hydrated ACC has been suggested based mainly on X-ray absorption spectroscopy (XAS) and nuclear magnetic resonance (NMR) data that show different local structures of ACC precipitated from solutions at different pH values: calcite-like ACC is obtained at pH≈8.75 and vaterite-like ACC precipitates from solutions of pH≈9.8 and higher. In addition to these two amorphous polymorphs, other studies have shown hints of aragonite local order in ACC from shells of freshwater snails, based on XAS data that show Ca-O coordination numbers of approximately 9, the theoretical value of aragonite.These results were reproduced in synthetic samples of ACC doped with Mg2+, suggesting a role of this cation in the selection of the ACC amorphous polymorph. © 2013, Wiley-Vch Verlag.