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Kinetics of anionic polymerization of β‐myrcene in hydrocarbon solvents
No full textThe kinetics of anionic polymerization of β‐myrcene initiated by sec‐butyllithium were examined in saturated and unsaturated hydrocarbon solvents, i.e. cyclohexane, cyclohexene, 4‐vinylcyclohexene and dl‐limonene. Polymerizations usually proceeded in a living manner, i.e. in the absence of termination and chain transfer reactions, in all solvents, to produce well‐defined polymyrcenes with high content (85%) of cis‐1,4 units. However, polymyrcenyllithium chains exhibited limited long‐term stability in 4‐vinylcyclohexene solution, most probably due to chain transfer to solvent. Reaction orders with respect to the concentration of active chains were found to be one‐quarter in cyclohexane increasing to one‐half in unsaturated solvents, indicating that the polymyrcenyllithium chains are present as tetrameric or dimeric associates, respectively. Apparent activation energies were found to be 81 kJ mol−1 in cyclohexane and 77 kJ mol−1 in dl‐limonene solution, which are close to the values obtained by quantum chemical calculations
Seasonal PFAS monitoring in surface water via complementary EOF (HR-CS-GFMAS) and target analytics
No full textThe aim of this study was to investigate seasonal shifts in PFAS contamination. Therefore, samples were collected from the River Spree to measure the level of extractable organically bound fluorine (EOF). This was achieved by employing high resolution-continuum source-graphite furnace molecular absorption spectrometry (HR-CS-GFMAS), a method for EOF surface water analysis first described by Metzger et al.. Complementary target-screenings were performed for a small set of relevant PFAS to achieve a more detailed look into the PFAS contamination over time and space and into the identifiable fraction of the EOF. Furthermore, hot spots of relevant PFAS pollution were identified in the river system
Sustainability features future flame retardancy: Microalgae phosphorus-enriched in wastewater and polylimonencarbonate
No full textRather environmentally friendly flame retardant bio-composites have become part of the state of the art. Using two illuminating examples the talk gives an outlook towards sustainability beyond “partly bio-carbon”. In waste water phosphorous-enriched microalgae are introduced as bio-based adjuvant in polylactide (PLA). The flame retardancy effect is discussed and compared with other novel bio-based additives. In a combination with a commercial flame retardant, half of the commercial flame retardant can be replaced without worsening the UL 94 classification V0. In the second example flame retardant routes for poly(limonene carbonate) are discussed. Poly(limonene carbonate) is synthesized with a bio-based monomer limonene oxide and CO2. A novel bio-based flame retardant melem phytate together with bio-based charring agents is proposed to realize a fully bio-based flame retardant poly(limonene carbonate)
Bioinspired Electrode Materials
No full textPorous carbon materials are known for their applicability in important areas such as sorption, catalysis and electrochemistry (e.g. fuel cell catalysts, supercapacitor or battery electrodes). It was shown that nitrogen doped carbons (NDCs) act as an inexpensive and highly active non-metal catalyst in the oxygen reduction reaction (ORR), with the potential to reach performances of practical need one day. A key strategy towards improvement for this aim comprises the generation of advantageous porosity, which typically means high surface area and mass transport pores as well as the control over the chemistry of catalytically active sites. My group developed novel sol-gel type strategies that are using molten salts or molten acids as unconventional reaction medium for the porogenesis in doped carbons, thereby revisiting classic activation techniques. Carbon materials with extra high surface area of ~2800 m2 g-1 and pore volumes, up to four times as high as in commercial activated carbons, are obtained. Hierarchical pore systems, like used in nature (leaves, lungs, etc.) facilitate some of the electrochemical performances. Moreover, because of the elements also defining organic matter, also binding motifs can be realized that are reminiscent of proteins/enzymes. We established the pyrolytic template-ion reaction using cations like Mg2+ and Zn2+ to imprint tetrapyrrolic N4 sites (like in the heme molecule), embedded into the carbon structure. The imprinted structure may be utilized as catalytically active site by performing ion-exchange reactions. This way catalytic activity can be tuned for different societal important reactions, but also the defined catalysts structure allows the assignment of structure-performance relations. Other “tricks” that nature uses, are to influence the passage of ions through cell walls, or to expel water molecules from catalytically active sites. I will show some recent work on carbon electrodes used as battery active materials that utilizes similar pathways
Regulations versus practice and the Divine Name: Ink analysis in medieval Torah scrolls
No full textThe medieval Rabbis had very strict rules for the construction of a Sefer Torah. The Divine Names should be written
• by a qualified scribe
• who is ritually pure
• in the presence of a minyan (10 adult Jewish men)
• in an appropriate frame of mind
• without being interrupted
However, when these scrolls were written it would have been impossible to verify any of this after the fact. While we do not currently have any way to determine how recently the scribes had bathed, or what they might have been thinking as they wrote, we can now know much more about the inscription of the Divine Name than these scribes ever would have guessed.
It is sometimes apparent from a visual inspection of the text that the Divine Name has been written in a second stage, from irregular letter kerning or a different ink colour. Using XRF, we have been able to discover more instances of a different ink used for the Name, and have shown that in some cases the secondary ink was also used to correct the main text, suggesting that the later writing was done by a master scribe who also proofread the entire scroll.
Using a Brucker M6 Jetstream, it has been possible to produce elemental “heat maps” of whole paragraphs or even large sections of a parchment sheet. Using such large samples of text, we can usefully compare the levels of copper and zinc used to write individual letters or words despite their relatively low concentration, which permits very fine differentiation of the inks used.
The techniques presented here would also be highly applicable to assessing ink degradation, as they are able to detect much smaller differences in ink composition than had previously been possible
Eine Frage der Technik? Verfahren und Kriterien für den sicheren Betrieb von Wasserstoffanlagen
No full textDas Webinar wird im Rahmen von TransHyDE Systemanalyse (AP5.3 Akzeptanzbewertungen) durchgeführt und adressiert aus einer interdisziplinären Perspektive relevante Aspekte der Sicherheit und öffentlichen Risikowahrnehmung von Wasserstoffprojekten. Dabei erfolgt ein Überblick über Standards der sicherheitstechnischen Forschung, Einblicke aus der Projektkommunikation mit Akteuren und Bürger*innen sowie die Vorstellung aktueller Forschungsergebnisse zur öffentlichen Wahrnehmung der Risiken von Wasserstofftechnologien. Die Diskussion geht den u.a. Fragen nach, welche Rolle das Thema Sicherheit in der aktuellen Planungspraxis spielt, wie transparent über Risiken kommuniziert werden kann, ohne Vertrauen zu gefährden und welche Kommunikationsansätze sich als zielführend zeigen, um gesellschaftlichen Unsicherheiten zu begegnen. Der Vortrag zeigt auf, dass der sichere Betrieb von Anlagen nicht nur mit der Technologie alleine gewährleistet werden kann
Electrochemical characterisation of degradation mechanisms in lithium- and sodium-ion batteries during overdischarge
No full textLithium-iron-phosphate (LFP) and sodium-ion batteries (SIBs) are promising technologies for energy storage systems due to their safe handling and cost-effectiveness. SIBs can be discharged to 0V without the safety concerns associated with lithium-ion batteries' copper current collector oxidation. However, overdischarging both types of batteries may decompose and subsequently rebuild the solid electrolyte interphase (SEI), leading to irreversible capacity loss and degradation.
This study performs an in-situ analysis of the overdischarge process of LiFePO4 pouch and Na-ion cylindrical cells. Therefore, the cells are characterised for three low C-rate constant current or three slow-scan voltage cycles. While the voltage range of the manufacturer’s specifications is chosen for the first and third cycle, for the second cycle the minimum voltage is modified to 0.5V (LFP) and 0V (SIB), respectively. This enables tracing the degradation during the overdischarge, as well as through a comparison of the results pre- and post-overdischarging. For this purpose, the study employs two electrochemical characterisation techniques: differential voltage analysis (DVA) and cyclic voltammetry (CV). While cyclic voltammetry allows for the study of the kinetics of electron transfers [1], DVA enables the assessment of lithium distribution homogeneity and capacity degradation [2].
In both cells, the characterisation shows significant differences before and after overdischarging, indicating lasting changes through the decomposition and rebuilding of the SEI. This comparative study elucidates the overdischarge-induced degradation in sodium- and lithium-ion batteries, highlighting the utility of CV and DVA in analysing degradation mechanisms
From support to shell: An innovative design of air-stable nano zero-valent iron–nickel catalysts via structural self-assembly
No full textThis work presents the design of air-stable core–shell zero-valent iron–nickel nanofilaments supported on silica and zeolite, developed to overcome the oxidation limitations of nano zero-valent iron in environmental catalysis. The nanofilaments feature ∼ 100 nm iron–nickel cores surrounded by ultrafine iron-rich threads embedded with aluminates and silicates, originating from partial support dissolution during synthesis. By varying the iron reduction time, three catalysts were prepared: one on silica reduced for 30 min, and two on zeolite reduced for 30 and 15 min. They were thoroughly characterized using nitrogen physisorption, X-ray diffraction, electron microscopy with elemental analysis, Mössbauer spectroscopy, and small-angle X-ray scattering. The zeolite-supported catalyst reduced for 15 min showed the highest activity for hexavalent chromium reduction (rate constant 8.054 min−1), attributed to a higher fraction of reactive iron–nickel phases formed under shorter reduction. Its tailored core–shell structure improves air stability and surface reactivity, highlighting its potential as a next-generation zero-valent iron nanocatalyst for aqueous remediatio
Bericht zum Fortschritt des laufenden Projekts: "Hybrider Einsatz von LTT-Schweißzusätzen zur Schwingfestigkeitsverbesserung hochfester Stahlbauteile"
No full textLow Transformation Temperature (LTT) Schweißzusätze erzeugen während der Abkühlung Druckeigenspannungen in die Schweißnaht und Wärmeeinflusszone durch eine Volumenexpansion, wodurch die Ermüdungsfestigkeit erhöht werden kann. Um das Potential dieser neuartigen Schweißzusätze besser zu quantifizieren, wurden konventionelle Längssteifen als Probenkörper verwendet, welche an den Stirnseiten mit einer LTT-Zusatznaht geschweißt wurden. Durch Variation der Schweißparameter konnten unterschiedliche Nahtformen realisiert werden. Es konnte, je nach Nahtausführung, eine Erhöhung der Ermüdungsfestigkeit bei 2 Millionen Lastwechseln von 140% festgestellt werden. Somit sind LTT-Zusätze grundsätzlich geeignet, um die Ermüdungsfestigkeit zu erhöhen. Weiterhin wurde festgestellt, dass das Reparaturschweißen mit LTT Schweißzusätzen als Decklage ebenfalls zu einem deutlichen Ermüdungsfestigkeitsanstieg führte
Down to Earth - Stampflehm
No full textDer Vortrag „Stampflehm“ gibt einen kurzen Überblick zur stofflichen Zusammensetzung von Stampflehm sowie zu verschiedenen Fertigungstechniken im Stampflehmbau. Es werden wichtige konstruktive Details erläutert und Hinweise bezüglich der Ausführung von Stampflehmwänden gegeben. Darüber hinaus wird das aktuell gültige Bemessungskonzept vorgestellt und dessen Schwachstellen aufgezeigt. Im Anschluss erfolgt eine Gegenüberstellung von Stampflehm mit verschiedenen Massivbauweisen hinsichtlich Tragfähigkeit, Schall- und Brandschutz sowie der Ökobilanz. Abschließend wird von aktuell laufenden Forschungsvorhaben im Bereich des Stampflehmbaus berichtet