TY - GEN A1 - Langner, Thomas A1 - Rietig, Anja A1 - Acker, Jörg T1 - Raman spectroscopic determination of the degree of dissociation of nitric acid in binary and ternary mixtures with HF and H2SiF6 T2 - Journal of Raman Spectroscopy N2 - The oxidizing effect of nitric acid in aqueous solutions depends on the concentration of undissociated nitric acid. This makes the concentration of undissociated nitric acid an essential parameter to monitor and control the quality of silicon etching in the industrial manufacturing of solar cells. In the present study, a method known already is extended in such a way that the degree of dissociation of nitric acid can be determined by Raman spectroscopy in HF/HNO3/H2SiF6 acid mixtures over a broad concentration range for the first time and without using an internal or external standard to compensate the typical time‐dependent drift of a Raman spectrometer. The method developed requires the calculation of a peak area ratio from the areas of the unimpeded Raman signals assigned to nitrate (νN − O) at 1,048 cm−1 and to undissociated HNO3 (νN − OH) at 957 cm−1. The correlation between the peak ratio and the degree of dissociation of nitric acid revealed can be described by a simple empirical equation. Using this equation, the degree of dissociation of nitric acid can be determined over a broad concentration range in binary and ternary mixtures of HNO3 with HF and H2SiF6. The impact of the acids HF and H2SiF6 and the total water content in the degree of dissociation of nitric acid is discussed. KW - Raman spectroscopy KW - nitric acid KW - dissociation KW - hexafluosilicic acid KW - hydrofluoric acid KW - silicon KW - etching Y1 - 2020 U6 - https://doi.org/10.1002/jrs.5769 VL - 51 IS - 2 SP - 366 EP - 372 ER - TY - GEN A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg ED - Andresen, Birger ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard ED - Page, Ingrid T1 - Advanced insights into the stoichiometry and kinetics of the reaction of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures T2 - Silicon for the Chemical and Solar Industry XV N2 - The stoichiometry and kinetics of wet chemical etching of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures was investigated. The side reactions and main reaction pathways were identified by quantifying all reaction products. The relationship between the concentration of undissociated HNO3 and the consumption of HNO3, as well as the formation of H2 as a function of the mixing ratios were found by varying the etching mixture composition systematically. Based on the etching rates determined, kinetic models for the reaction- and diffusion-controlled reaction mechanism are presented as well as the interrelation between the etchant composition and the transition between reaction- and diffusion-controlled etching. KW - silicon KW - etching KW - Raman KW - etch rate KW - mass spectrometry KW - hydrogen KW - nitrous gases Y1 - 2020 SN - 978-82-997357-9-7 SP - 145 EP - 159 PB - The Norwegian University of Science and Technology CY - Trondheim ER - TY - GEN A1 - Rietig, Anja A1 - Grafe, Hans-Joachim A1 - Acker, Jörg T1 - New insights into boron species in acidic digestion solutions of boron-doped silicon T2 - Journal of Analytical Atomic Spectrometry N2 - The exact and precise determination of the boron concentration in silicon is still a challenge. A systematic investigation dealing with the digestions of 60 silicon samples with HF-HNO3 and subsequent boron determination by ICP-OES revealed that the concentration found could be up to 60% lower than the actual boron concentration depending on the composition of the sample solution. As the original boron–silicon compound that was identified was colloidally precipitated in the presence of an excess of hydrofluoric acid and then partially retained by filtration or by the sample introduction system, systematic lower boron concentrations were determined. In acidic, HF-free digestion solutions, this compound existed in a soluble form parallel to the borate in B(OH)4−. In an excess of hydrofluoric acid, the compound was converted into the colloidal form and, in parallel, B(OH)4− was converted to tetrafluoroborate, BF4−. For the composition of the colloidal compound, a molar ratio of boron to silicon of 1 : 4 could be determined. 11B-ss-NMR analysis revealed a tetrahedral geometry compound with a central boron atom surrounded by four silicon atoms. It is assumed that a soluble form with four –Si(OH)3 groups was present in the hydrofluoric acid-free solutions, while an insoluble form with four –SiF3 groups was present in HF-containing solution. KW - silicon KW - ICP-OES KW - etching KW - hydrofluoric acid KW - nitric acid KW - 11B-NMR KW - high-precision chemical analysis KW - boron KW - digestion Y1 - 2021 UR - https://pubs.rsc.org/en/content/articlelanding/2021/ja/d1ja00190f SN - 1364-5544 VL - 36 IS - 11 SP - 2492 EP - 2500 ER - TY - GEN A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg T1 - Comprehensive stoichiometric studies on the reaction of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures T2 - Physical chemistry, chemical physics KW - silicon KW - etching KW - stoichiometry KW - hydrogen KW - nitrogen oxides KW - mechanism Y1 - 2022 UR - https://pubs.rsc.org/en/content/articlelanding/2022/cp/d1cp05418j U6 - https://doi.org/10.1039/d1cp05418j SN - 1463-9076 VL - 24 IS - 5 SP - 3094 EP - 3108 ER - TY - GEN A1 - Rietig, Anja A1 - Grafe, Hans-Joachim A1 - Acker, Jörg T1 - Understanding the Reasons for Erroneous Determinations of Boron in Silicon following Wet Chemical Digestion in HF/HNO3 T2 - Proceedings of the Silicon for the Chemical & Solar Industry XVI KW - boron KW - silicon KW - species KW - trace element Y1 - 2022 UR - https://ssrn.com/abstract=4123058 SN - 978-82-692919-0-2 U6 - https://doi.org/10.2139/ssrn.4123058 ER - TY - CHAP A1 - Rietig, Anja A1 - Acker, Jörg T1 - Ressourcensicherung durch Recycling von Sekundärrohstoffen T2 - Systemwissen für die vernetzte Energie- und Mobilitätswende KW - Recycling KW - Lithium-Ionen-Batterien KW - Elektroschrott KW - Edelmetalle Y1 - 2022 UR - https://www.ibbf.berlin/assets/images/Dokumente/220627_IBBF_Kompendium_2022_WEB_final%20(1).pdf SN - 978-3-9816861-8-0 SP - 141 EP - 152 PB - Vereinigung für Betriebliche Bildungsforschung e.V. CY - Berlin ET - 2. Auflage ER - TY - GEN A1 - Langner, Thomas A1 - Sieber, Tim A1 - Rietig, Anja A1 - Merk, Virginia A1 - Pfeiffer, Lutz A1 - Acker, Jörg T1 - A Phenomenological and Quantitative View on the Degradation of Positive Electrodes from Spent Lithium-ion Batteries in Humid Atmosphere T2 - Scientific Reports N2 - The present study deals with the phenomenological observation of the corrosion of the positive electrode foil of lithium-ion batteries containing LiNi0.6Co0.2Mn0.2O2 (NMC) as cathode material. Due to the presence of moisture, localized water accumulation is formed on the NMC surface. The water absorbed by the electrolyte reacts with the NMC under Li+/H+ exchange and the resulting pH increase leads to dissolution of the carrier foil and characteristic salt-like blooms on the NMC surface. With the increase in the relative area occupied by the holes in the aluminum foil per time, a sufficiently suitable parameter was found with which to quantitatively determine the extent of corrosion. The degree of degradation depends on time and ambient humidity. It was shown that functional recycling with the water jet method is no longer applicable for degraded foils, since the mechanical stability of the foils decreases as corrosion progresses. Lithium, aluminum, sulfur and oxygen were detected in the blooms using SEM–EDX and Laser-Induced-Breakdown-Spectroscopy (LIBS). The underlying NMC layer was found to contain mainly aluminum and significantly lower lithium content than the non-degraded material. SEM and Raman microscopy analyses also showed that the active material is also locally degraded and therefore no longer suitable for functional recycling. KW - Analytical chemistry KW - lithium KW - cathode KW - materials KW - LIBS KW - Raman KW - SEM-EDX KW - degradation Y1 - 2023 U6 - https://doi.org/10.1038/s41598-023-32688-0 SN - 2045-2322 VL - 13 ER - TY - GEN A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg T1 - About determining reliable etching rates and the role of temperature in kinetic experiments on acidic wet chemical etching of silicon T2 - Physical Chemistry Chemical Physics Y1 - 2023 UR - https://pubs.rsc.org/en/content/articlelanding/2023/cp/d2cp05837e U6 - https://doi.org/10.1039/D2CP05837E SN - 1463-9084 VL - 25 IS - 16 SP - 11387 EP - 11397 ER - TY - GEN A1 - Rietig, Anja A1 - Acker, Jörg T1 - Kinetic studies on acidic wet chemical etching of silicon in binary and ternary mixtures of HF, HNO3 and H2SiF6 T2 - Physical Chemistry Chemical Physics Y1 - 2023 U6 - https://doi.org/10.1039/d3cp03188h SN - 1463-9084 SN - 1463-9076 VL - 25 IS - 38 SP - 26245 EP - 26257 ER -