Browsing by Author "Kappen, P"

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    An EXAFS and XANES study of V, Ni, and Fe speciation in cokes for anodes used in aluminum production
    (The Minerals, Metals & Materials Society, 2020) Jahrensenge, G; Wells, HC; Sommerseth, C; Ratvik, AP; Lossius, LP; Sizeland, KH; Kappen, P; Svennson, AM; Haverkamp, RG
    The main ingredient in pre-baked carbon anodes used in the aluminum industry, is petroleum coke. Today, the aluminum industry faces challenges regarding the availability of what is considered anode grade coke. The increasing amount of impurities (e.g. sulfur and metals) in the crude oil end up in the low-quality product, coke. Petroleum coke that can be used in the aluminum production is calcined, producing calcined petroleum coke (CPC), and coke that have previously only been used as fuel, needs to be considered for CPCs, despite the high impurity content [1]. Impurities in coke are known to affect certain reactions in the cell; sulfur is believed to reduce CO2 reactivity, while metals are suggested as catalyzers increasing the CO2 and air reactivity [2]. The exact mechanisms of these reactions are not known but can be assumed to depend on the chemical composition of the impurities. The chemical sulfur compounds in CPC are known to mainly be organically polycyclic thiophenes and thiazines, as part of the carbon sheets [3, 4]. Metals have been assumed to be present as organic complexes, similarly to the compounds found in crude oil [5], but the nature of the metals have not previously been determined. Previous investigations by the authors [6], using synchrotron radiation, identified significant quantities of an additional sulfur compound to the mentioned organic sulfur. This was identified as a compound with S-S bonds, possibly including metal sulfides, but the high amount quantified in some cokes did not correlate to the metal content in the respective cokes. Further investigations on metal speciation in cokes were therefore suggested. X-ray absorption spectroscopy (XAS) techniques were discovered to be applicable to CPCs to decide the chemical compounds of the metals V, Ni, and Fe. By comparing the recorded fluorescence spectra of cokes to those of known compounds, using the X-ray absorption near edge structure (XANES) region of the spectra, Ni and Fe were suggested to be metal sulfides, and possibly some metal porphyrin. Using the extended X-ray absorption fine structure (EXAFS) region, and comparing to information on local structure, i.e. nearest atoms and bond lengths associated with variable space groups, found in large databases, all three metals were discovered to be bound as hexagonal metal sulfides (V3S4, NiS and FeS respectively). The metal sulfides were also discovered to be highly dispersed in the cokes, and not present as inclusions [7].
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    An EXAFS and XANES study of V, Ni, and Fe speciation in cokes for anodes used in aluminum production
    (The Minerals, Metals & Materials Society, 2020-02-23) Jahrsengene, G; Wells, HC; Sommerseth, C; Ratvik, AP; Lossius, LP; Sizeland, KH; Kappen, P; Svensson, AM; Haverkamp, RG
    The main ingredient in pre-baked carbon anodes used in the aluminum industry, is petroleum coke. Today, the aluminum industry faces challenges regarding the availability of what is considered anode grade coke. The increasing amount of impurities (e.g. sulfur and metals) in the crude oil end up in the low-quality product, coke. Petroleum coke that can be used in the aluminum production is calcined, producing calcined petroleum coke (CPC), and coke that have previously only been used as fuel, needs to be considered for CPCs, despite the high impurity content [1]. Impurities in coke are known to affect certain reactions in the cell; sulfur is believed to reduce CO2 reactivity, while metals are suggested as catalyzers increasing the CO2 and air reactivity [2]. The exact mechanisms of these reactions are not known but can be assumed to depend on the chemical composition of the impurities. The chemical sulfur compounds in CPC are known to mainly be organically polycyclic thiophenes and thiazines, as part of the carbon sheets [3, 4]. Metals have been assumed to be present as organic complexes, similarly to the compounds found in crude oil [5], but the nature of the metals have not previously been determined. Previous investigations by the authors [6], using synchrotron radiation, identified significant quantities of an additional sulfur compound to the mentioned organic sulfur. This was identified as a compound with S-S bonds, possibly including metal sulfides, but the high amount quantified in some cokes did not correlate to the metal content in the respective cokes. Further investigations on metal speciation in cokes were therefore suggested. X-ray absorption spectroscopy (XAS) techniques were discovered to be applicable to CPCs to decide the chemical compounds of the metals V, Ni, and Fe. By comparing the recorded fluorescence spectra of cokes to those of known compounds, using the X-ray absorption near edge structure (XANES) region of the spectra, Ni and Fe were suggested to be metal sulfides, and possibly some metal porphyrin. Using the extended X-ray absorption fine structure (EXAFS) region, and comparing to information on local structure, i.e. nearest atoms and bond lengths associated with variable space groups, found in large databases, all three metals were discovered to be bound as hexagonal metal sulfides (V3S4, NiS and FeS respectively). The metal sulfides were also discovered to be highly dispersed in the cokes, and not present as inclusions [7].
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    High-accuracy transmission and fluorescence XAFS of zinc at 10 K, 50 K, 100 K and 150 K using the hybrid technique
    (International Union of Crystallography, 2022-10-24) John, MW; Sier, D; Ekanayake, RSK; Schalken, MJ; Tran, CQ; Johannessen, B; de Jonge, MD; Kappen, P; Chantler, CT
    The most accurate measurements of the mass attenuation coefficient for metals at low temperature for the zinc K-edge from 9.5 keV to 11.5 keV at temperatures of 10 K, 50 K, 100 K and 150 K using the hybrid technique are reported. This is the first time transition metal X-ray absorption fine structure (XAFS) has been studied using the hybrid technique and at low temperatures. This is also the first hybrid-like experiment at the Australian Synchrotron. The measured transmission and fluorescence XAFS spectra are compared and benchmarked against each other with detailed systematic analyses. A recent method for modelling self-absorption in fluorescence has been adapted and applied to a solid sample. The XAFS spectra are analysed using eFEFFIT to provide a robust measurement of the evolution of nanostructure, including such properties as net thermal expansion and mean-square relative displacement. This work investigates crystal dynamics, nanostructural evolution and the results of using the Debye and Einstein models to determine atomic positions. Accuracies achieved, when compared with the literature, exceed those achieved by both relative and differential XAFS, and represent a state-of-the-art for future structural investigations. Bond length uncertainties are of the order of 20–40 fm. © Open Access - CC BY 4.0 licence
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    Research in art and archaeology: capabilities and investigations at the Australian Synchrotron
    (Taylor & Francis, 2019-11-26) Brand, HEA; Howard, DL; Huntley, J; Kappen, P; Masimenko, A; Paterson, DJ; Puskar, L; Tobin, MJ
    In the Australian Synchrotron's short history, we have made some important advances in instruments and capabilities that can be employed to study art and archaeology. In this article, we describe the capabilities at the Australian Synchrotron that are well-suited to investigating art, archaeology, and cultural heritage. We also present some case studies that demonstrate the breadth and impact of science that has been performed by researchers using these capabilities. Synchrotron radiation has many advantages that make it ideally suited to investigating art, archaeology and cultural heritage. The broad spectrum of radiation that can be employed and, in particular, the penetrating nature of the radiation at hard X-ray energies give the ability to conduct 3D reconstruction with tomography. In many cases, the techniques can be non-destructive and performed in situ. The intense infrared radiation allows infrared microscopy at diffraction-limited resolution and the recently developed attenuated total internal reflection mode can probe the surface of very delicate samples. In the following, we describe the relevant beamlines, their capabilities, and then illustrate with some key examples of research, from paleobotany to the investigation of paintings. © 2019 Informa UK Limited