TY - GEN A1 - Rietig, Anja A1 - Acker, Jörg T1 - Development and validation of a new method for the precise and accurate determination of trace elements in silicon by ICP-OES in high silicon matrices T2 - Journal of Analytical Atomic Spectrometry N2 - A new method for the accurate and precise determination of impurities in silicon was developed and statistically validated. Particular attention was paid to the correct determination of the non-metals boron and phosphorus. Instead a time-consuming open vessel digestion under mild conditions, the dissolution of silicon took place in a microwave-assisted high-pressure system. The essential innovation of the presented method is the direct use of the concentrated digestion solution for ICP-OES measurements. This approach avoids the commonly used, time-consuming method that requires the removal of silicon and acid matrix by volatilisation, which is the most critical step in the determination of boron; however, the ICP-OES measurement in such high silicon matrices requires an entirely new optimisation of the measuring conditions, including the careful selection of emission lines with respect to selectivity and, spectral and non-spectral inferences. For quantification of the impurities contents, the methods of matrix matching (MMC) and multiple standard addition (MSA) were used. After optimisation of the spike concentrations for MSA, the qualities of both methods were compared through a statistical analysis. For the metallic impurities Al, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zr and P, the validation was performed against certified reference materials (IPT134, IPT135, NIST57b). To validate boron, 9 silicon samples with different contents of boron from three interlaboratory comparisons were used. The new procedure allows for the determination of the impurities of 4N-silicon (12 elements). KW - impurities KW - inductively coupled plasma emission spectroscopy KW - silicon KW - microwave-assisted digestion KW - high silicon matrix KW - multiple standard addition KW - boron KW - phosphorus Y1 - 2017 UR - http://pubs.rsc.org/en/content/articlelanding/2017/ja/c6ja00241b#!divAbstract U6 - https://doi.org/10.1039/C6JA00241B VL - 32 IS - 2 SP - 322 EP - 333 ER - TY - GEN A1 - Grafe, Hans-Joachim A1 - Löser, Wolfgang A1 - Schmitz, Steffen A1 - Sakaliyska, Miroslava A1 - Wurmehl, Sabine A1 - Eisert, Stefan A1 - Reichenbach, Birk A1 - Acker, Jörg A1 - Rietig, Anja A1 - Ducke, Jana T1 - NMR investigation of boron impurities in refined metallurgical grade silicon T2 - Physica status solidi. A, Applications and Materials Science N2 - The nuclear magnetic resonance (NMR) method was applied for tracking boron impurities in the refining process of metallurgical grade (MG) silicon. From the NMR signal of the 11B isotope at an operating temperature 4.2 K, the boron concentration can be estimated down to the order of 110 wppm B. After melting and resolidification of MG-Si alloyed with Ca and Ti, a major fraction of B impurities remains in the Si solid solution as inferred from the characteristic NMR frequency. The alloying element Ti does not form substantial fractions of TiB2. Acid leaching of crushed powders of MG-Si alloyed with Ca and Ti can diminish the initial impurity content of B suggesting its accumulation in the grain boundary phases. KW - boron KW - impurity KW - intermetallic compounds KW - nuclear magnetic resonance KW - silicon KW - transition-metal diboride KW - Si-Al melt KW - removal KW - solidification Y1 - 2015 UR - http://onlinelibrary.wiley.com/doi/10.1002/pssa.201431908/full U6 - https://doi.org/10.1002/pssa.201431908 SN - 1862-6319 VL - 212 IS - 9 SP - 2031 EP - 2036 ER - TY - CHAP A1 - Acker, Jörg A1 - Ducke, Jana A1 - Rietig, Anja A1 - Müller, Tim A1 - Eisert, Stefan A1 - Reichenbach, Birk A1 - Löser, Wolfgang ED - Oye, Harald A. ED - Brekken, Harald ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard T1 - Segregation, grain boundary milling, and chemical leaching for the refinement of metallurgical-grade silicon for photovoltaic application T2 - Silicon for the Chemical and Solar Industry XII, Trondheim, 2014 N2 - The present work describes a completely new approach to the solidification refinement of metallurgical-grade silicon. The new process comprises the following steps: (i) The first step involves adding auxiliary metals to the molten silicon in order to segregate the metallic and non-metallic impurities in the secondary phase after cooling. (ii) The melt is rapidly cooled in the cellular solidification regime. This generates a Si microstructure with a defined cell size in which all cell boundaries are surrounded by the secondary phase. Furthermore, the secondary phase should form an interconnected three-dimensional network. (iii) The solids are crushed by shockwaves using electrohydraulic fragmentation techniques. The shockwaves lead to preferential crushing at the interface between the silicon and the secondary phase. (iv) The secondary phases are fast and effectively removed by microwave-assisted high-pressure leaching that was newly developed for this process. The potential of the new refinement procedure is demonstrated with auxiliary metals Ca, Al, and Ti. This new procedure yields a significant decrease in phosphorous and metal impurities. KW - silicon KW - leaching KW - hydrometallurgy KW - solar cell KW - segregation KW - etching Y1 - 2014 SN - 978-82-997357-8-0 SP - 177 EP - 188 PB - Department of Materials Science and Engineering, Norwegian University of Science and Technology CY - Trondheim ER - TY - CHAP A1 - Rietig, Anja A1 - Acker, Jörg ED - Nygaard, Lars ED - Pachaly, Bernd ED - Page, Ingrid Gamst ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard T1 - A new and fast method for determination of boron, phosphorus and other trace elements in metallurgical grade silicon T2 - Silicon for the Chemical and Solar Industry XIII, Kristiansand, 2016 N2 - A new method for accurate and precise determination of non-metallic and metallic impurities in silicon was developed and statistically validated. The first step is the fast dissolution of silicon in a microwave-assisted high pressure system to minimize a loss of phosphorus. The essential innovation is the use of the concentrated digestion solution for ICP-OES measurements. This approach avoids the common removal of the silicon and acid matrix by volatilization, which can cause considerable losses of boron. Finally, for the ICP-OES measurements in such high-silicon matrices the optimum measuring conditions were determined and a careful selection of emission lines with respect to selectivity, spectral and non-spectral inferences and matrix effects was performed. The method of matrix matched calibration (MMC) is used for quantification of the impurities’ contents. For Al, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zr and P the validation was performed against certified reference materials (IPT134, IPT135, NIST57b). To validate the determination of boron 9 silicon samples of different boron contents from three interlaboratory comparisons were used. The new procedure allows the determination of impurities of 4N-silicon (12 elements) with high precision and accuracy. KW - silicon KW - ICP-OES KW - impurity KW - chemical analysis KW - boron KW - phosphorus Y1 - 2016 UR - https://www.ntnu.no/trykk/publikasjoner/Silicon%20for%20the%20chemical%20and%20solar%20industry%20XIII/ SP - 95 EP - 106 PB - Department of Materials Science and Engineering, Norwegian University of Science and Technology CY - Trondheim ER - TY - CHAP A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg ED - Scheschkewitz, David ED - Kickelbick, Guido T1 - Dissolution of silicon in HF/HNO3 mixtures: A revised model T2 - 9th European Silicon Days, 9-12 September 2018, Saarbrücken, Germany, Book of abstracts N2 - The dissolution of Si in HF/HNO3 consists of a set of complex reactions and thus a large number of reaction products. The most comprehensive picture of this reaction, the role of the involved reaction products and the reactivity of the HF/HNO3 mixtures depending on their composition is drawn by Steinert et al..[1]-[3] Based on the first systematic investigations on hydrogen formation by Hoffmann et al.[4], Acker et al. succeeded a first mass and electron balance for the reaction of silicon in HF/HNO3.[5] However, there is still a lack in interpretation of the mass end electron balances arising from several nitrous oxides. So far, the identified nitrogen oxides NO, NO2 and N2O were considered in sum[5] and neither separated nor individually studied or quantified. The aim of this work is to complete the mass and electron balance by the contribution of the individual nitrous oxides and to identify their individual formation pathways. Kinetic measurements of the NO and NO2 formation during the dissolution of Si, NO2 turns out as a result from the oxidation of the primary product NO by the HNO3 in the etching mixtures. Subsequently, NO and NO2 react to N2O3 dissolved in the acid mixture. The kinetics of both reactions were individually studied by bubbling NO in HF/HNO3 mixtures of different composition. The already identified intermediary species N4O62+ turns out to be formed by disproportionation of dissolved NO2 via N2O4 without dissolution of silicon. A detailed kinetic studied showed, that only dissolved N2O3 and not the intermediate N4O62+ contribute to the dissolution rate of silicon in HF/HNO3 acid mixtures. Finally, kinetic measurements revealed that the formed H2 reduces gaseous NO yielding to the final gaseous reaction products N2, N2O as well as to ammonium ions which all are formed with identical reaction rate. This reaction is assumed to proceed via NH2OH as intermediate. As result of the identification and quantification of intermediary and final reaction products a new reaction scheme needs to be established leading to a new approach to the mass and electron balance for the oxidation of silicon during the dissolution in HF/HNO3 mixtures. KW - silicon KW - etching KW - Raman spectroscopy KW - mass spectrometry KW - gas analysis KW - reaction mechanism Y1 - 2018 SP - S. 199 PB - Universität des Saarlandes CY - Saarbrücken ER - TY - GEN A1 - Sieber, Tim A1 - Ducke, Jana A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg T1 - Recovery of Li(Ni0.33Mn0.33Co0.33)O2 from Lithium-Ion Battery Cathodes: Aspects of Degradation T2 - Nanomaterials N2 - Nickel–manganese–cobalt oxides, with LiNi0.33Mn0.33Co0.33O2 (NMC) as the most prominent compound, are state-of-the-art cathode materials for lithium-ion batteries in electric vehicles. The growing market for electro mobility has led to a growing global demand for Li, Co, Ni, and Mn, making spent lithium-ion batteries a valuable secondary resource. Going forward, energy- and resource-inefficient pyrometallurgical and hydrometallurgical recycling strategies must be avoided. We presented an approach to recover NMC particles from spent lithium-ion battery cathodes while preserving their chemical and morphological properties, with a minimal use of chemicals. The key task was the separation of the cathode coating layer consisting of NMC, an organic binder, and carbon black, from the Al substrate foil. This can be performed in water under strong agitation to support the slow detachment process. However, the contact of the NMC cathode with water leads to a release of Li+ ions and a fast increase in the pH. Unwanted side reactions may occur as the Al substrate foil starts to dissolve and Al(OH)3 precipitates on the NMC. These side reactions are avoided using pH-adjusted solutions with sufficiently high buffer capacities to separate the coating layer from the Al substrate, without precipitations and without degradation of the NMC particles. KW - lithium KW - nickel–manganese–cobalt oxide KW - NMC KW - leaching KW - recycling KW - SEM-EDX KW - Raman spectroscopy KW - lithium ion battery Y1 - 2019 UR - https://www.mdpi.com/journal/nanomaterials/special_issues/charact_nano UR - https://www.mdpi.com/2079-4991/9/2/246 U6 - https://doi.org/10.3390/nano9020246 SN - 2079-4991 VL - 9 IS - 2 SP - 246 EP - 259 ER - TY - CHAP A1 - Rietig, Anja A1 - Acker, Jörg T1 - Ressourcensicherung durch Recycling von Sekundärrohstoffen T2 - Systemwissen für die vernetzte Energie- und Mobilitätswende KW - Lithiumbatterie KW - Funktionelles Recycling KW - Nickel-Mangan-Cobalt-Oxid KW - NMC KW - Raman-Spektroskopie KW - Laugung Y1 - 2019 SN - 978-3-9816861-7-3 SP - 170 EP - 181 PB - Vereinigung für Betriebliche Bildungsforschung e.V. CY - Berlin ET - 1. Auflage ER - TY - GEN A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg T1 - A revised model of silicon oxidation during the dissolution of silicon in HF/HNO₃ mixtures T2 - Physical chemistry, chemical physics N2 - The stoichiometry of wet chemical etching of silicon in concentrated HF/HNO₃ mixtures was investigated. The formation of nitrogen species enriched in the etching mixture and their reactivity during the etching process was studied. The main focus of the investigations was the comprehensive quantification of the gaseous reaction products using mass spectrometry. Whereas previously it could only be speculated that nitrogen was a product, its formation was detected for the first time. The formation of hydrogen, N₂, N₂O and NH₄⁺ showed a dependence on the etching bath volume used, which indicates the formation of nitrogen compounds by side reactions. Simultaneously, the ratio of the nitrogen oxides, NO and NO₂, formed decreases with increasing etching bath volume, while nitric acid consumption increases, so that the formation of NO₂ could also be identified as a side reaction. Based on the stoichiometries obtained, a new reaction scheme for the reduction of nitric acid during etching in HF/HNO₃ mixtures and an electron balance for the oxidation of silicon is presented. KW - silicon KW - etching KW - mechanism KW - nitrogen oxide KW - hydrogen KW - mass spectrometry KW - Raman spectroscopy KW - kinetics Y1 - 2019 UR - https://pubs.rsc.org/en/content/articlelanding/2019/CP/C9CP04429A#!divAbstract U6 - https://doi.org/10.1039/c9cp04429a SN - 1463-9076 VL - 21 SP - 22002 EP - 22013 ER - TY - GEN A1 - Sieber, Tim A1 - Rietig, Anja A1 - Ducke, Jana A1 - Acker, Jörg ED - Vogt, Carla T1 - Direkte Feststoffanalyse von Hauptkomponenten in Kathodenmaterialien von Lithiumbatterien mittels HRCS-GF-AAS T2 - Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts N2 - Zur Bestimmung der metallischen Hauptkomponenten in Lithium-Batterie-Kathodenmaterialien ist der nasschemische Aufschluss mit anschließender ICP-OES-Analyse oft das Mittel der Wahl. Da dieses Verfahren jedoch recht zeitaufwendig ist und den Einsatz starker Säuren erfordert, wurde eine Methode zur direkten Feststoffanalyse mittels HRCS-GF-AAS (high resolution continuum source graphit furnace atom absorption spectrometry) nach dem STPF-Konzept (stabilized temperature platform furnace) entwickelt. Die hohen Analytkonzentrationen erfordern dabei die Messung auf den vergleichsweise wenig intensiven Linien Li = 323,2657 nm, Ni = 294,3912 nm, Mn = 321,6945 nm und Co= 243,5823 nm. Zusätzlich wird das Probenmaterial einer Feststoffverdünnung mit matrixverwandten Komponenten unterzogen. Die Verdünnung senkt zum einen die Konzentration und die Gefahr der Verschleppung der Analyten und begünstigt zum anderen die Freigabe des Analyten aus der Probenmatrix. Durch Aufnahme von Extinktions-Zeit-Verläufen im Temperaturbereich von 200 - 2600 °C konnten die Freisetzungstemperaturen für jeden Analyten bestimmt werden. Nach anschließenden Optimierungen der Pyrolyse- und Atomisierungstemperaturen wurde mithilfe der Einzeloxide für jeden Analyten die Linearität des Messsignals geprüft und der Arbeitsbereich festgelegt. Durch Vermessung von variierenden Oxidmischungen und Mischoxiden, sowie Zusatz möglicher weiterer Interferenten, wie dem Bindermaterial PVDF wurden Spezifität, Selektivität und Robustheit der Methode überprüft. Abschließend erfolgte anhand realer Proben (Recyclinggut aus Lithium-Batterie-Kathoden) ein Vergleich zwischen den Ergebnissen der direkten Feststoffanalyse mittels HRCS-GF-AAS und dem bereits etablierten Verfahren der ICP-OES Analyse nach nasschemischem Aufschluss. Nach umfangreicher Methodenentwicklung kann ein Verfahren der direkten Feststoffanalyse von Recylinggut aus Kathodenmaterialien von Lithium-Ionen-Batterien mittels HRCS-GF-AAS bereitgestellt werden, das eine schnelle und präzise Analyse der Hauptkomponenten Li, Ni, Mn und Co erlaubt. KW - continuum source KW - AAS KW - Feststoffanalytik KW - Feststoffstandard KW - Graphitrohr KW - Interferenz KW - NMC KW - Recycling KW - Lithium KW - Batterie Y1 - 2019 UR - https://tu-freiberg.de/en/canas/canas-2019-engl/final-program VL - 2019 SP - S1/4 PB - TU Bergakademie Freiberg CY - Freiberg ET - 1. Auflage ER - TY - GEN A1 - Acker, Jörg A1 - Sieber, Tim A1 - Ducke, Jana A1 - Langner, Thomas A1 - Rietig, Anja T1 - Degradation effects on Li(Ni0.33Mn0.33Co0.33)O2 in the recovery of lithium battery cathodes T2 - Advanced Lithium Batteries for Automobile Applications - ABAA 12, Book of Abstracts N2 - The compound Li(Ni0.33Mn0.33Co0.33)O2 (NMC) is the state-of-the-art lithium-ion battery cathode material. Due to the increasing demand NMC is of crucial economically importance for the worldwide emerging market of electromobility. Recycling of end-of-life lithium-ion batteries to recover NMC, in particular of batteries from automotive vehicles, is one future strategy to save costs and to become more independent from the supply of the essential elements Co and Mn. Several concepts for NMC recycling from lithium-ion batteries are based on wet-chemical process steps, in particular, to separate the NMC containing cathode layer from the underlying metal foil. However, NMC is very sensitive against the attack by water and reagents that are added to promote the separation process. The present study deals with the wet-chemical recycling of NMC using aqueous reagent solutions in a under varying process conditions. The recovered NMC samples are characterized in order to study the ongoing degradation at the surface of the NMC particles. In particular, two major degradation pathways are identified: (i) a preferential loss of lithium and nickel and (ii) the formation of passivation layers due to unwanted side reactions. DRIFT measurements are performed to study the NMC surface species after the recovery processes. SEM/EDX mappings are used to detect changes in the chemical composition in the surface region of the chemically treated NMC particles. Finally, a detailed study of the changes in the chemical state at the NMC particle surface is done by Raman microscopy by means of the deconvolution of the recorded spectra into their A1G component (representing the metal-oxide phonons) and into the Eg component (representing the oxide-metal-oxide phonons). As result of this study, the consequences of different wet-chemical process conditions on the quality of the recovered NMC material are discussed. KW - lithium ion battery KW - recycling KW - NMC KW - electromobility KW - degradation KW - Raman spectroscopy KW - cathode Y1 - 2019 SP - 28 PB - Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg CY - Ulm ET - 1. Auflage ER -