TY - JOUR A1 - Stroh, Julia A1 - Schlegel, Moritz-Caspar A1 - Schmidt, Wolfram A1 - Nguyen, Thi Yen A1 - Meng, Birgit A1 - Emmerling, Franziska T1 - Time-resolved in situ investigation of Portland cement hydration influenced by chemical admixtures N2 - Numerous admixtures are used in the building practice to customize the properties of the cement paste during application. The influences of admixtures on the course of cement hydration and formation of hydrate phases have to be considered. Polycarboxylate ether (PCE) based polymeric superplasticizers (SPs) are known to retard the setting of the cement paste. The extent of the retardation differs depending on the molecular structure of the SP. Additionally, the presence of a stabilizing agent (SA) in the cement paste has a retarding side effect on the setting. The initial cement hydration processes and the detailed mechanisms of the retardation influenced by PCEs, as well as their interactions with particular SAs, are insufficiently understood. Up to now, only the results of phenomenological studies were taken into account to describe this retardation process. A detailed structure analysis monitoring the change of the phase composition during the hydration was never applied. Both SP and SA affect the adsorption of the sulphate ions on the clinker particles, causing changes in the formation of ettringite during the initial hydration, and are therefore a crucial part of the setting process itself. Here, the initial hydration of cement influenced by the interaction of SP and SA was monitored in situ by synchrotron X-ray diffraction. The high time resolution of the measurements allowed a continuous detection of the hydrates formed. The hydration was followed from the starting point of water addition and for couple of hours afterwards. The hydration of the levitated cement pellets containing starch as SA was initialized by adding aqueous solutions of different commercial SPs. Changes in the ettringite formation were detected in comparison to the reference hydration of pure cement. KW - Synchrotron KW - Portland cement Initial hydration KW - Superplasticizer KW - Stabilizer KW - XRD PY - 2016 DO - https://doi.org/http://dx.doi.org/10.1016/j.conbuildmat.2015.12.097 IS - 106 SP - 18 EP - 26 PB - Elsevier AN - OPUS4-35467 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Geburtig, Anja A1 - Wachtendorf, Volker A1 - Schmidt, Anita A1 - Goedecke, Thomas T1 - Combined impact of UV radiation and nitric acid on HDPE containers during outdoor exposure T1 - Kombinierte Einwirkung von UV-Strahlung und Salpetersäure auf HDPE-Behälter bei der Freibewitterung N2 - Unpigmented HDPE jerrycans filled with nitric acid (55%) and water respectively had been exposed to outdoor conditions for one Berlin summer season. As both liquids underwent equal temperature progression, exposure effects of UV radiation and nitric acid as well as of their combination can be separated and compared. On the basis of various property changes after these exposures, synergistic action is evaluated and compared to a damaged Intermediate Bulk Container (IBC) from a transport accident. It is found that carbonyl formation goes along with lightness increase in color measurement due to microcracking and with a worsening in mechanical behavior, all of them showing synergistic effects of UV and nitric acid exposure. In contrast, embedding nitrogen compounds goes along with yellowing of the material but cannot be correlated to oxidation. The reason for intensified damaging is the decomposition of the 55-percent nitric acid and formation of nitrogen oxides even at ambient temperatures, caused by UV radiation. Thus, damaging effects become similar to those caused by fuming nitric acid exposure at temperatures above 60 °C, with the result of strong oxidative degradation of the polyethylene. In contrast, exclusive exposure to the 55-percent nitric acid at 40 °C does not cause any failure. It can therefore be assumed that also the damaged IBC had been exposed to both UV radiation and nitric acid, probably outdoors. KW - Polyethylene KW - Nitric acid KW - UV radiation KW - Outdoor weathering KW - Resistance PY - 2018 DO - https://doi.org/10.3139/120.111148 SN - 0025-5300 VL - 60 IS - 3 SP - 257 EP - 264 PB - Carl Hanser Verlag CY - München AN - OPUS4-44567 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Anita A1 - Schlick-Hasper, Eva A1 - Geburtig, Anja A1 - Bethke, John T1 - Stand der BAM-Forschungsvorhaben T2 - Erfahrungsaustausch Verpackungen CY - Berlin DA - 2014-09-16 PY - 2014 AN - OPUS4-32638 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, B.V.K.J. A1 - Fechler, N. A1 - Falkenhagen, Jana A1 - Lutz, J.-F. T1 - Controlled folding of synthetic polymer chains through the formation of positionable covalent bridges N2 - Covalent bridges play a crucial role in the folding process of sequence-defined biopolymers. This feature, however, has not been recreated in synthetic polymers because, apart from some simple regular arrangements (such as block co-polymers), these macromolecules generally do not exhibit a controlled primary structure—that is, it is difficult to predetermine precisely the sequence of their monomers. Herein, we introduce a versatile strategy for preparing foldable linear polymer chains. Well-defined polymers were synthesized by the atom transfer radical polymerization of styrene. The controlled addition of discrete amounts of protected maleimide at precise times during the synthesis enabled the formation of polystyrene chains that contained positionable reactive alkyne functions. Intramolecular reactions between these functions subsequently led to the formation of different types of covalently folded polymer chains. For example, tadpole (P-shaped), pseudocyclic (Q-shaped), bicyclic (8-shaped) and knotted (α-shaped) macromolecular origamis were prepared in a relatively straightforward manner. KW - Copolymerization KW - Chain folding KW - SEC KW - NMR KW - FT-IR KW - LAC KW - MALDI PY - 2011 DO - https://doi.org/10.1038/NCHEM.964 SN - 1755-4330 SN - 1755-4349 VL - 3 SP - 234 EP - 238 PB - Nature Publishing Group CY - London, UK AN - OPUS4-23888 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Hentschel, Manfred P. A1 - Lück, S. A1 - Schmidt, V. A1 - Hilger, A. A1 - Garcia-Moreno, F. A1 - Manke, I. T1 - Reconstruction of limited view tomography data by DIRECTT N2 - Incomplete tomographic data sets such as limited view (missing wedge) data represent a well-known challenge for reconstruction algorithms, since they unavoidably lead to substantial image artefacts. Such data sets may occur in industrial computed tomography of limited access (e.g. extended components, fixed objects), directional opacity, limited sample life time or laminographic set-up. We present strategies to effectively suppress the typical elongation artefacts (e.g. lemon-like deformed pores) by our iterative algorithm DIRECTT which offers the opportunity to vary the versatile reconstruction parameters within each cycle. Those strategies are applied to experimental data obtained from metallic foams as well as model simulations. Comparison is drawn to state-ofthe-art techniques (filtered backprojection and algebraic techniques). Further reference is made to reconstructions of complete data sets serving as gold standards. For quantitative assessment of the reconstruction quality adapted techniques based on spatial statistics are introduced. T2 - 18th WCNDT - World conference on nondestructive testing CY - Durban, South Africa DA - 16.04.2012 KW - Computed tomography KW - Limited tomographic data KW - Iterative reconstruction KW - DIRECTT KW - Limited view KW - Missing wedge KW - Spatial statistics PY - 2012 UR - http://www.ndt.net/article/wcndt2012/papers/208_wcndtfinal00208.pdf SN - 978-0-620-52872-6 SP - 1 EP - 9 AN - OPUS4-25834 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schulz, K. A1 - Schmack, R. A1 - Klemm, H. W. A1 - Kabelitz, Anke A1 - Schmidt, T. A1 - Emmerling, Franziska A1 - Kraehnert, R. T1 - Mechanism and kinetics of hematite crystallization in air: Linking bulk and surface models via mesoporous films with defined nanostructure N2 - Iron can form numerous oxides, hydroxides, and oxide−hydroxides. Despite their relevance, many of the transformation processes between these phases are still poorly understood. In particular the crystallization of quasi-amorphous hydroxides and oxide−hydroxides is difficult to assess, since typical diffraction and scattering methods provide only sampleaveraged information about the crystallized phases. We report a new approach for the investigation of the crystallization of oxide−hydroxides. The approach relies on model-type films that comprise a defined homogeneous nanostructure. The nanostructure allows quantitative linking of Information obtained by bulk-averaging diffraction techniques (XRD, SAXS) with locally resolved information, i.e., Domain sizes (SEM, TEM, LEEM) and phase composition (SAED). Using time-resolved imaging and diffraction we deduce mechanism and kinetics for the crystallization of ferrihydrite into hematite. Hematite forms via nucleation of hematite domains and subsequent Domain growth that terminates only upon complete transformation. A Johnson−Mehl−Avrami−Kolmogorov model describes the kinetics over a wide temperature range. The derived understanding enables the first synthesis of ferrihydrite films with ordered mesoporosity and quantitative control over the films’ hematite and ferrihydrite content. KW - Iron oxide KW - Crystallization KW - Mesoporous films KW - Nanostructure PY - 2017 DO - https://doi.org/10.1021/acs.chemmater.6b05185 SN - 0897-4756 SN - 1520-5002 VL - 29 IS - 4 SP - 1724 EP - 1734 AN - OPUS4-39690 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lueck, S. A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Hentschel, Manfred P. A1 - Schmidt, V. T1 - Statistical comparison of various reconstruction algorithms with respect to missing wedge artifacts in computed tomography N2 - The presence of elongation, streak and blurring artifacts in tomograms recorded under a missing wedge of rotation angles presents a major challenge for the quantitative analysis of tomographic image data. We show that the missing wedge artifacts of standard reconstruction algorithms may be reduced by the innovative reconstruction technique DIRECTT. For the comparison of missing wedge artifacts we apply techniques from spatial statistics, which have been specifically designed to investigate the shape of phase boundaries in tomograms. KW - X-ray tomography KW - Scanning transmission electron microscopy (STEM) KW - Structural PY - 2012 DO - https://doi.org/10.1557/opl.2012.209 SN - 0272-9172 VL - 1421 SP - 1 EP - 6 PB - North-Holland Publ. Co. CY - New York, NY AN - OPUS4-25468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Raute, J. A1 - Schmidt, J. A1 - Bhadeliya, A. A1 - Rehmer, B. A1 - Olbricht, J. A1 - Jokisch, T. A1 - Biegler, M. A1 - Rethmeier, M. T1 - Investigation on seam quality and fatigue crack propagation in electron beam welded additive manufactured Inconel 939 N2 - Laser powder bed fusion of metals (PBF-LB/M) offers great potential for the production of new and spare parts for stationary gas turbines made of nickel superalloys such as Inconel 939 (IN939). In order to enable integration into existing assemblies and overcome design limitations, the additive manufacturing process chain must be expanded by suitable joining techniques. This study compares the electron beam welding of cast IN939 sheets and sheets produced additively using PBF-LB/M. The investigation focuses on the achievable seam quality with regard to geometric irregularities and internal defects in the form of liquation cracks on the microscale in the heat-affected zone. The evaluation of the welded samples shows no differences in the formation of the seam shape between the additively manufactured material and the cast material. For both materials, the highest quality category for beam-welded seams according to DIN EN ISO 13,919–1 was achieved at high welding speeds of 20 mm/s. Regardless of the manufacturing method, both materials show an increase in crack formation with increasing welding speed. However, due to its microstructure, the PBF-LB/M material exhibits significantly fewer microcracks overall. Final crack propagation tests on welded PBF-LB/M samples that were treated using HIP also show stable crack growth without sudden failure, which opens up potential for practical application. KW - Electron beam welding KW - Inconel 939 KW - PBF-LB/M KW - Liquation cracking KW - Fatigue crack propagation PY - 2026 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-657015 DO - https://doi.org/10.1016/j.jajp.2026.100389 SN - 2666-3309 VL - 13 SP - 1 EP - 10 PB - Elsevier B.V. AN - OPUS4-65701 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -