TY - JOUR A1 - Weller, Andreas A1 - Zhang, Z. A1 - Slater, L. A1 - Kruschwitz, Sabine A1 - Halisch, M. T1 - Induced polarization and pore radius — A discussion N2 - Permeability estimation from induced polarization (IP) measurements is based on a fundamental premise that the characteristic relaxation time τ is related to the effective hydraulic radius reff controlling fluid flow. The approach requires a reliable estimate of the diffusion coefficient of the ions in the electrical double layer. Others have assumed a value for the diffusion coefficient, or postulated different values for clay versus clay-free rocks. We have examined the link between a widely used single estimate of τ and reff for an extensive database of sandstone samples, in which mercury porosimetry data confirm that reff is reliably determined from a modification of the Hagen-Poiseuille equation assuming that the electrical tortuosity is equal to the hydraulic tortuosity. Our database does not support the existence of one or two distinct representative diffusion coefficients but instead demonstrates strong evidence for six orders of magnitude of variation in an apparent Diffusion coefficient that is well-correlated with reff and the specific surface area per unit pore volume Spor. Two scenarios can explain our findings: (1) the length scale defined by τ is not equal to reff and is likely much longer due to the control of pore-surface roughness or (2) the range of diffusion coefficients is large and likely determined by the relative proportions of the different minerals (e.g., silica and clays) making up the rock. In either case, the estimation of reff (and hence permeability) is inherently uncertain from a single characteristic IP relaxation time as considered in this study. KW - Spectral induced polarisation KW - Pore radius KW - Permeability KW - Specific surface KW - Mercury intrusion PY - 2016 DO - https://doi.org/10.1190/GEO2016-0135.1 SN - 0016-8033 SN - 1942-2156 VL - 81 IS - 5 SP - D519 EP - D526 AN - OPUS4-38393 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, Zhiyang A1 - Merk, V. A1 - Müller, Anja A1 - Unger, Wolfgang A1 - Kneipp, Janina T1 - Role of metal cations in plasmon-catalyzed oxidation: A case study of p-aminothiophenol dimerization N2 - The mechanism of the plasmon-catalyzed reaction of p-aminothiophenol (PATP) to 4,4′-dimercaptoazobenzene (DMAB) on the surface of metal nanoparticles has been discussed using data from surface-enhanced Raman scattering of DMAB. Oxides and hydroxides formed in a plasmon-catalyzed process were proposed to play a central role in the reaction. Here, we report DMAB formation on gold nanoparticles occurring in the presence of the metal cations Ag+, Au3+, Pt4+, and Hg2+. The experiments were carried out under conditions where formation of gold oxide or hydroxide from the nanoparticles can be excluded and at high pH where the formation of the corresponding oxidic species from the metal ions is favored. On the basis of our results, we conclude that, under these conditions, the selective oxidation of PATP to DMAB takes place via formation of a metal oxide from the ionic species in a plasmon-catalyzed process. By evidencing the necessity of the presence of the metal cations, the reported results underpin the importance of metal oxides in the reaction. KW - Metal ions KW - Plasmonic catalysis KW - p-aminothiophenol KW - 4,4'-dimercaptoazobenzene KW - Surface-enhanced Raman scattering PY - 2017 UR - http://pubs.acs.org/doi/abs/10.1021/acscatal.7b02700 DO - https://doi.org/10.1021/acscatal.7b02700 SN - 2155-5435 N1 - Geburtsname von Müller, Anja: Hermanns, A. - Birth name of Müller, Anja: Hermanns, A. VL - 7 IS - 11 SP - 7803 EP - 7809 PB - American Chemical Society CY - Washington AN - OPUS4-43001 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, Zeyu A1 - Weller, Andreas A1 - Kruschwitz, Sabine T1 - Pore radius distribution and fractal dimension derived from spectral induced polarisation N2 - The pore size distribution provides a suitable description of the pore space geometry that can be used to investigate the fractal nature of the pore space or to determine a fractal dimension. Fractal dimension describes the size of geometric objects as a function of resolution. It can be integrated into models of permeability prediction. We investigated the fractal dimension of the pore volume of 11 Eocene sandstone samples from China. This study describes an approach to use spectral induced polarisation spectra to estimate the pore size distribution and to determine the fractal dimension of the pore volume. Additionally, the fractal dimension was derived from data of the capillary pressure curves from mercury intrusion and the transversal relaxation time distribution of nuclear magnetic resonance. For samples with an effective pore radius larger than 1 μm, good agreement exists between the values of fractal dimension derived from the three different methods, which implies the identification of similar pore structures. Spectral induced polarisation can be a non-invasive laboratory technique for the estimation of the pore size distribution, but the application of the methodology for field measurements remains a challenging problem considering the limited frequency range. KW - Pore radius distribution KW - Fractal dimension KW - Spectral induced polarization PY - 2017 DO - https://doi.org/10.3997/1873-0604.2017035 SN - 1569-4445 VL - 15 IS - 6 SP - 625 EP - 632 PB - Wiley AN - OPUS4-43250 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Huang, A1 - Zheng, A1 - Zhang, A1 - Lu, A1 - Wang, A1 - Kunte, Hans-Jörg A1 - Sand, W. T1 - Long Term Temperature and Humidity Evolution Forecast in Near Field of Nuclear Waste Container N2 - The paper aims to simulate the corrosion environment of nuclear waste containers at different geological disposal periods to obtain temperature and humidity information at the interface between the container and the surrounding environment. The simulated data and calculation results of long term temperature evolution at the surface of nuclear waste (HLW) containers from some typical nuclear countries about the safety disposition were reviewed. Combining different burial patterns, this paper speculated the long term temperature evolution rule for China. According to the study about saturation variation of buffer/backfill material at home and abroad, the humidity evolution of bentonite at the surface of HLW containers was specu- lated. The study showed that the temperature of the container surface increased rapidly at the beginning, and gradually decreased after the climax. For safety reasons, the maximum temperature was designed below 100°C. The saturation of bentonite was af- fected by the mutual influences of the heat released by nuclear waste decay and the infiltration of groundwater. It was dominated by the released heat in the early stage, and later was influenced greatly by the infiltration of groundwater. It is generally believed that the water content at the surface of the container will increase obviously in about 3 years, and will be saturated in about 10 years. The prediction of long-term temperature and humidity evolution will lay a foundation for study of corrosion evolution of nuclear waste containers in China. KW - Corrosion evolution KW - Nuclear waste KW - Disposal repository KW - Temperature and humidity PY - 2018 SN - 1672-9242 VL - 15 IS - 10 SP - 109 EP - 113 PB - Zhongguo Bingqi Gongye di-wujiu Yanjiusuo CY - Chongqing AN - OPUS4-46953 LA - zho AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Huang, Y.-L. A1 - Zheng, A1 - Zhang, A1 - Lu, A1 - Wang, A1 - Kunte, Hans-Jörg A1 - Sand, W. T1 - Forecast on Long Term Chemical Environment Evolution on Surface of Nuclear Waste Container N2 - Surface environment changes of nuclear waste container, mainly including oxygen contents, buffer pore water components and pH under the conditions of “borehole” type and “In-floor” type with bentonite buffer/backfill and concrete buffer were summarized. This summarization provides a basic corrosion environment reference for the corrosion evolution re- search of high-level radioactive waste disposal repository in our country. KW - Corrosion evolution KW - Nuclear waste KW - Disposal repository KW - Corrosion environment PY - 2018 DO - https://doi.org/10.7643/ issn.1672-9242.2018.10.017 SN - 1672-9242 VL - 15 IS - 10 SP - 103 EP - 108 PB - Zhongguo Bingqi Gongye di-wujiu Yanjiusuo CY - Chongqing AN - OPUS4-46952 LA - zho AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ewert, Uwe A1 - Zscherpel, Uwe A1 - Vogel, Justus A1 - Zhang, F. A1 - Long, N.X. A1 - Nguyen, T.P. T1 - Visibility of Image Quality Indicators (IQI) by Human Observers in Digital Radiography in Dependence on Measured MTFs and Noise Power Spectra N2 - Digital radiographic images were analysed to predict the visibility of image quality indicators (IQI), based on normalized noise power spectra (NNPP) and modulation transfer function (MTF) measurements. The fixed pattern noise of some digital detectors result in different noise spectra, which influence the visibility of different IQIs, depending on the hole diameter. Studies, based on measurement of basic spatial resolution and contrast to noise ratio were performed together with presampled MTF measurements and the NNPS in dependence on the spatial frequency. Plate hole IQIs, step hole IQIs, and equivalent penetrameter sensitivity (EPS) IQIs based on ASTM E 746 were measured to verify the influence of the different parameters. Modelling of digital images was used to verify the applied numeric tools. A study has been performed for imaging plates and digital detector arrays to analyse differences. Formulas for the prediction of the visibility functions for hole type IQIs are derived. In consequence the standards for characterization and classification of computed radiography (ASTM E 2446) and radiography with DDAs (ASTM E 2597) need to be revised. T2 - 12th ECNDT 2018 CY - Gothenburg, Sweden DA - 11.06.2018 KW - Image evaluation KW - Computed radiography (CR) KW - Digital Detector Array (DDA) KW - Detail detection PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-473486 UR - www.ndt.net/?id=22967 SN - 1435-4934 VL - 23 IS - 8 SP - 1 EP - 7 PB - NDT.net CY - Kirchwald AN - OPUS4-47348 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ewert, Uwe A1 - Zscherpel, Uwe A1 - Zhang, F. A1 - Long, N.X. A1 - Phong, N. T1 - Essentielle Parameter zur numerischen Abschätzung der Sichtbarkeit von Bildgüteprüfkörpern in der digitalen Radiographie N2 - Die Voraussetzungen für die Vorhersage der Sichtbarkeit von Bildgüteprüfkörpern (BPK) wurden seit Beginn der kommerziellen Anwendung der technischen Radiographie diskutiert und in diversen nationalen und internationalen Standards festgeschrieben. Diese Fragen werden nach Einführung der digitalen Radiographie und der CT wieder neu diskutiert. Draht BPKs wurden in Deutschland seit 1935 (DIN 1915: 1935) und später in den meisten europäischen Ländern benutzt. In den USA und Frankreich wurden vorzugsweise BPKs mit Löchern verwendet (ASTM E 1025 seit 1984 oder E 1742 seit 1992 bzw. die Vorgängernorm MIL STD-543 seit 1962). Jetzt werden auch die Umrechnungsnormen zur Erkennbarkeit von Draht zu Loch-BPKs in Frage gestellt. ISO 19232-3, der französische RCCM-Kode einerseits und ASTM E 747 und ASME BPVC Section V Tab. T-276 andererseits unterscheiden sich erheblich bei den Anforderungen im Bereich hoher Wandstärken (Hochenergieradiographie). Untersuchungen dazu werden vorgestellt. Mit Einführung der digitalen Detektoren ändern sich auch die Rauschspektren. Durch die Herstellung werden insbesondere bei Speicherfolien "Rauschmuster" eingeprägt, die bei hohen Belichtungsdosen sichtbar werden. Diese veränderten Rauschspektren ergeben auch veränderte Erkennungsparameter für menschliche Bildauswerter. Hierzu wurden an ausgewählten Detektoren MTFs (presampled) und normierte Rauschspektren gemessen. Erweiterte Erkennbarkeits-Formeln zur Vorhersage der Sichtbarkeit von BPKs für Bildauswerter und erste Ergebnisse werden vorgestellt. T2 - DGZfP-Jahrestagung 2018 CY - Leipzig, Germany DA - 07.05.2018 KW - Image quality KW - Computed radiography (CR) KW - Digital Detector Array (DDA), KW - Sichtbarkeit von Anzeigen PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-473496 UR - www.ndt.net/?id=23069 VL - 2018 SP - 1 EP - 14 PB - Deutsche Gesellschaft für zerstörungsfreie Prüfung e.V. (DGZfP) AN - OPUS4-47349 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kneipp, Janina A1 - Zhang, Zhiyang T1 - Mapping the Inhomogeneity in Plasmonic Catalysis on Supported Gold Nanoparticles Using Surface-Enhanced Raman Scattering Microspectroscopy N2 - The characterization of a catalyst often occurs by averaging over large areas of the catalyst material. On the other hand, optical probing is easily achieved at a resolution at the micrometer scale, specifically in microspectroscopy. Here, using surface-enhanced Raman scattering (SERS) mapping of larger areas with micrometer-sized spots that contain tens to hundreds of supported gold nanoparticles each, the photoinduced dimerization of p-aminothiophenol (PATP) to 4,4′-dimercaptoazobenzene (DMAB) was monitored. The mapping data reveal an inhomogeneous distribution of catalytic activity in the plasmon-catalyzed reaction in spite of a very homogeneous plasmonic enhancement of the optical signals in SERS. The results lead to the conclusion that only a fraction of the nanostructures may be responsible for a high catalytic activity. The high spot-to-spot variation in catalytic activity is also demonstrated for DMAB formation by the plasmon-catalyzed reduction from p-nitrothiophenol (PNTP) and confirms that an improvement of the accuracy and reproducibility in the characterization of catalytic reactions can be achieved by microspectroscopic probing of many positions. Using SERS micromapping during the incubation of PATP, we demonstrate that the reaction occurs during the incubation process and is influenced by different parameters, leading to the conclusion of dimerization in a gold-catalyzed, nonphotochemical reaction as an alternative to the plasmon-catalyzed process. The results have implications for the future characterization of new catalyst materials as well as for optical sensing using plasmonic materials. KW - P-aminothiophenol KW - Silver nanoparticles KW - Chemical transformation KW - Metal nanoparticles KW - Coupling reactions KW - AU nanoparticle KW - AG nanoparticle KW - Spectroscopy KW - Sers KW - Molecule PY - 2018 DO - https://doi.org/10.1021/acs.analchem.8b01701 VL - 90 IS - 15 SP - 9199 EP - 9205 PB - American Chemical Society AN - OPUS4-46372 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, Z. A1 - Kruschwitz, Sabine A1 - Weller, A. A1 - Halisch, M. T1 - Enhanced pore space analysis by use of µ-CT, MIP, NMR, and SIP N2 - We investigate the pore space of rock samples with respect to different petrophysical parameters using various methods, which provide data on pore size distributions, including micro computed tomography (µ-CT), mercury Intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and spectral-induced polarization (SIP). The resulting cumulative distributions of pore volume as a function of pore size are compared. Considering that the methods differ with regard to their limits of resolution, a multiple-length-scale characterization of the pore space is proposed, that is based on a combination of the results from all of these methods. The approach is demonstrated using samples of Bentheimer and Röttbacher sandstone. Additionally, we compare the potential of SIP to provide a pore size distribution with other commonly used methods (MIP, NMR). The limits of Resolution of SIP depend on the usable frequency range (between 0.002 and 100 Hz). The methods with similar Resolution show a similar behavior of the cumulative pore volume distribution in the verlapping pore size range. We assume that µ-CT and NMR provide the pore body size while MIP and SIP characterize the pore throat size. Our study Shows that a good agreement between the pore radius distributions can only be achieved if the curves are adjusted considering the resolution and pore volume in the relevant range of pore radii. The MIP curve with the widest range in Resolution should be used as reference. KW - Pore space KW - Induced polarization KW - Mercury intrusion porosimetry KW - µ-CT KW - NMR PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-465071 DO - https://doi.org/10.5194/se-9-1225-2018 SN - 1869-9510 SN - 1869-9529 VL - 9 IS - 6 SP - 1225 EP - 1238 PB - Copernicus Publications CY - Göttingen AN - OPUS4-46507 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zhang, Zeyu A1 - Weller, Andreas T1 - Beobachtung der Trocknung von Gesteinen mit Spektraler Induzierter Polarisation N2 - Bei der Trocknung von Gesteinen vermindert sich der Anteil des Wasservolumens im Porenraum, der als Sättigung bezeichnet wird. Mit abnehmender Sättigung sinkt die elektrische Leitfähigkeit des Gesteins. Die Abhängigkeit der elektrischen Leitfähigkeit von der Sättigung wird durch ein Potenzgesetz entsprechend der 2. Archie-Gleichung beschrieben: log(#CHR:sigma_LOWER#)=n log(Sw), wobei n der Sättigungsexponent ist. Bei der Trocknung von Gesteinen muss beachtet werden, dass die Wasserleitfähigkeit mit abnehmender Sättigung zunimmt, da die Konzentration der im Wasser gelösten Salze ansteigt. Das hat zur Folge, dass die bei Trocknungsexperimenten bestimmten Sättigungsexponenten deutlich kleiner sind als bei Verdrängungsexperimenten (z.B. Wasser durch Öl) mit gleichbleibender Wasserleitfähigkeit. Bei der Spektral(en) Induzierten Polarisation wird die komplexe elektrische Leitfähigkeit des Gesteins als Funktion der Frequenz betrachtet. Für den Real- und Imaginärteil der elektrischen Leitfähigkeit werden unterschiedliche Sättigungsexponenten bestimmt. Wir haben an zwei Sandsteinproben (Langenauer und Gravenhorster Sandstein) und einem Baumberger Kalksandstein Trocknungsexperimente durchgeführt. Die Sättigung wurde schrittweise von 100 % bis auf 10 % reduziert. In jeder Sättigungsstufe wurden an den Proben die Spektren der komplexen elektrischen Leitfähigkeit aufgezeichnet. Unsere Experimente zeigen, dass die Sättigungsexponenten für den Imaginärteil der komplexen elektrischen Leitfähigkeit mit 1,23 bis 1,59 deutlich größer sind als die des Realteils mit Werten zwischen 0,41 und 0,90. Dieser Unterschied resultiert aus der Tatsache, dass der Imaginärteil der Leitfähigkeit weniger stark mit zunehmender Wasserleitfähigkeit ansteigt als der Realteil. Für den Realteil der elektrischen Leitfähigkeit wird nach der 1. Archie-Gleichung ein linearer Zusammenhang zwischen Wasserleitfähigkeit und Gesteinsleitfähigkeit erwartet. Der Anstieg des Imaginärteils mit der Wasserleitfähigkeit kann mit einem Potenzgesetz mit einem Exponenten zwischen 0.1 und 0.62 beschrieben werden. Unsere Experimente zeigen, dass der Imaginärteil der elektrischen Leitfähigkeit wesentlich deutlicher auf die Austrocknung von Gesteinen reagiert und damit ein wirksamer Indikator zur Überwachung von Sättigungsänderungen sein kann. T2 - Jahrestagung der Deutschen Geophysikalischen Gesellschaft CY - Leoben, Austria DA - 12.2.2018 KW - Spektral induzierte Polarisation KW - Sandsteine KW - Trocknung PY - 2018 AN - OPUS4-45000 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, Zhiyang A1 - Gernert, U. A1 - Gerhardt, R. F. A1 - Höhn, E.-M. A1 - Belder, D. A1 - Kneipp, Janina T1 - Catalysis by Metal Nanoparticles in a Plug-In Optofluidic Platform: Redox Reactions of p-Nitrobenzenethiol and p-Aminothiophenol N2 - The spectroscopic characterization by surface-enhanced Raman scattering (SERS) has shown great potential in studies of heterogeneous catalysis. We describe a plug-in multifunctional optofluidic platform that can be tailored to serve both as a variable catalyst material and for sensitive optical characterization of the respective reactions using SERS in microfluidic systems. The platform enables the characterization of reactions under a controlled gas atmosphere and does not present with limitations due to nanoparticle adsorption or memory effects. Spectra of the gold-catalyzed reduction of p-nitrothiophenol by sodium borohydride using the plug-in probe provide evidence that the borohydride is the direct source of hydrogen on the gold surface, and that a radical anion is formed as an intermediate. The in situ monitoring of the photoinduced dimerization of p-aminothiophenol indicates that the activation of oxygen is essential for the plasmon-catalyzed oxidation on gold nanoparticles and strongly supports the central role of metal oxide species. KW - Gaseous reactants KW - Heterogeneous catalysis KW - Microfluidics KW - Optofluidics KW - Radicals KW - Reusable KW - Surface-enhanced Raman scattering (SERS) PY - 2018 UR - https://pubs.acs.org/doi/10.1021/acscatal.8b00101 DO - https://doi.org/10.1021/acscatal.8b00101 VL - 8 IS - 3 SP - 2443 EP - 2449 PB - American Chemical Society CY - Washington, DC, USA AN - OPUS4-44628 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, Luman A1 - de Greef, Nils A1 - Kalinka, Gerhard A1 - Van Bilzen, Bart A1 - Locquet, Jean-Pierre A1 - Verpoest, Ignaas A1 - Won Seo, Jin T1 - Carbon nanotube-grafted carbon fiber polymer composites: Damage characterization on the micro scale N2 - Multiwall carbon nanotubes (CNTs) e carbon fibers (CFs)hybrid materials were produced by directly growing CNTs on CFs by means of chemical vapor deposition. For the latter, the oxidative dehydrogenation reaction of C2H2 and CO2 was applied, which allows growing CNTs without damaging the CF surface. Uni-directional nano-engineered carbon fiber reinforced composites (nFRCs) were fabricated by impregnating these hybrid materials with epoxy. The nFRCs subjected to single fiber push-out tests revealed a decrease of the interfacial shear strength (IFSS) of about 36% compared to the carbon fiber composites without CNTs. By means of transverse three-point bending tests performed on pre-notched composite beams inside a scanning electron microscope, the fracturing behavior parallel to the fibers was studied in-situ. The nFRCs showed significantly reduced fiber/matrix debonding while CNTs pull-out, CNTs bridging as well as matrix failure occurred. These results demonstrate that the presence of CNTs in nFRCs affects the stress distribution and consequently the damage Initiation as well as the damage propagation. The presence of CNTs suppresses the stress concentration at the fiber/Matrix interface and reduces the debonding of CFs from the matrix. However, our results indicate that the stress concentration shifts towards the CNTs' ends/matrix interface and causes promoted matrix failure leading to lower IFSS. KW - Carbon fibres nanotubes interface PY - 2017 DO - https://doi.org/10.1016/j.compositesb.2017.06.004 SN - 1359-8368 SN - 1879-1069 VL - 126 SP - 202 EP - 210 PB - Elsevier CY - Niederlande AN - OPUS4-42202 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Veh, Georg A1 - Wang, Björn G. A1 - Zirzow, Anika A1 - Schmidt, Christoph A1 - Lützow, Natalie A1 - Steppat, Frederic A1 - Zhang, Guoqing A1 - Vogel, Kristin A1 - Geertsema, Marten A1 - Clague, John J. A1 - Korup, Oliver T1 - Progressively smaller glacier lake outburst floods despite worldwide growth in lake area N2 - Glacier lake outburst floods (GLOFs) may originate from larger lakes as these continue to grow with ongoing glacier retreat; however, this perception remains poorly supported in available GLOF databases. Here we mapped the areas of 1,686 glacier lakes, just before they drained, across 13 glaciated mountain regions outside polar regions and examined the trends in pre-GLOF lake areas between 1990 and 2023. We found that pre-GLOF lake areas barely changed, or even decreased, regionally through time, even as the total lake area, and thus hazard potential, grew overall. This counterintuitive finding reflects limits to growing GLOF magnitudes, such as the decoupling of lakes and parent glaciers, the development of wide, low-gradient outlets or human management. Across all regions, pre-GLOF lake areas depend on a few ice-dammed lakes, which have produced ten times more reported outbursts and ten times larger outbursts than moraineand bedrock-dammed lakes. The latter two dam types will continue to impound growing amounts of meltwater, thereby accounting for most of the overall GLOF hazard potential, while ice-dammed lakes will shrink with deglaciation. As these lake types will evolve differently in the twenty-first century, we call for customized simulations of GLOF outflows and impacts, given the growing exposure of critical infrastructure. KW - Climate change KW - Bayesian hierachical modelling KW - Outbursts flood PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-625709 DO - https://doi.org/10.1038/s44221-025-00388-w SN - 2731-6084 SP - 1 EP - 25 AN - OPUS4-62570 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, Kun A1 - Lin, Chang A1 - Pan, Lisha T1 - Effect of sisal fibers on the rheology of cement paste plasticized by polycarboxylate superplasticizer N2 - Sisal fibers (SF) and polycarboxylate superplasticizers (PCE) contribute to the sustainable development of cementitious materials by improving and optimizing their hardening properties. In this study, the impact of SF and PCE on the workability of cement pastes was investigated. The workability was evaluated through spreading diameter, yield stress, and plastic viscosity measurements, and the adsorption behavior of PCE was analyzed. The results showed that the introduction of SF had a negative effect on the workability of PCE plasticized cement pastes, reducing flowability and increasing yield stress and plastic viscosity, regardless of aspect ratio or dosage. A contact angle tester and a scanning electron microscope (SEM) were employed to examine the surface properties of SF. The mechanism behind this interaction of cement-PCE-SF was explored and found to be due to the rough surface of SF, which increased the consumption of PCE, and the formation of hydrogen bonds between PCE and SF. Additionally, PCE modified the interfacial structure between SF and the cement matrix, strengthening the relationship between the different phases. These findings provide new insights into the modification of fiber-reinforced cementitious materials. KW - Cement paste KW - Polycarboxylate KW - Flowability KW - Rheological KW - Sisal fiber (SF) KW - Adsorption PY - 2024 DO - https://doi.org/10.1061/jmcee7.mteng-16789 SN - 0899-1561 VL - 36 IS - 3 SP - 1 EP - 12 PB - American Society of Civil Engineers (ASCE) CY - Reston, VA AN - OPUS4-62893 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, Runze A1 - Sur, Debashish A1 - Li, Kangming A1 - Witt, Julia A1 - Black, Robert A1 - Whittingham, Alexander A1 - Scully, John R. A1 - Hattrick-Simpers, Jason T1 - Bayesian assessment of commonly used equivalent circuit models for corrosion analysis in electrochemical impedance spectroscopy N2 - Electrochemical Impedance Spectroscopy (EIS) is a crucial technique for assessing corrosion of metallic materials. The analysis of EIS hinges on the selection of an appropriate equivalent circuit model (ECM) that accurately characterizes the system under study. In this work, we systematically examined the applicability of three commonly used ECMs across several typical material degradation scenarios. By applying Bayesian Inference to simulated corrosion EIS data, we assessed the suitability of these ECMs under different corrosion conditions and identified regions where the EIS data lacks sufficient information to statistically substantiate the ECM structure. Additionally, we posit that the traditional approach to EIS analysis, which often requires measurements to very low frequencies, might not be always necessary to correctly model the appropriate ECM. Our study assesses the impact of omitting data from low to medium-frequency ranges on inference results and reveals that a significant portion of low-frequency measurements can be excluded without substantially compromising the accuracy of extracting system parameters. Further, we propose simple checks to the posterior distributions of the ECM components and posterior predictions, which can be used to quantitatively evaluate the suitability of a particular ECM and the minimum frequency required to be measured. This framework points to a pathway for expediting EIS acquisition by intelligently reducing low-frequency data collection and permitting on-the-fly EIS measurements. KW - Electrochemical Impedance Spectroscopy (EIS) KW - MAPz@BAM KW - Bayesian Inference KW - Corrosion PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-623392 DO - https://doi.org/10.1038/s41529-024-00537-8 VL - 8 SP - 120 PB - Springer Materials AN - OPUS4-62339 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, Fengchan A1 - Oiticica, Pedro Ramon Almeida A1 - Abad-Arredondo, Jaime A1 - Arai, Marylyn Setsuko A1 - Oliveira, Osvaldo N. A1 - Jaque, Daniel A1 - Fernandez Dominguez, Antonio I. A1 - de Camargo, Andrea Simone Stucchi A1 - Haro-González, Patricia T1 - Brownian Motion Governs the Plasmonic Enhancement of Colloidal Upconverting Nanoparticles N2 - Upconverting nanoparticles are essential in modern photonics due to their ability to convert infrared light to visible light. Despite their significance, they exhibit limited brightness, a key drawback that can be addressed by combining them with plasmonic nanoparticles. Plasmon-enhanced upconversion has been widely demonstrated in dry environments, where upconverting nanoparticles are immobilized, but constitutes a challenge in liquid media where Brownian motion competes against immobilization. This study employs optical tweezers for the three-dimensional manipulation of an individual upconverting nanoparticle, enabling the exploration of plasmon-enhanced upconversion luminescence in water. Contrary to expectation, experiments reveal a long-range (micrometer scale) and moderate (20%) enhancement in upconversion luminescence due to the plasmonic resonances of gold nanostructures. Comparison between experiments and numerical simulations evidences the key role of Brownian motion. It is demonstrated how the three-dimensional Brownian fluctuations of the upconverting nanoparticle lead to an “average effect” that explains the magnitude and spatial extension of luminescence enhancement. KW - Upconversion KW - Plasmon enhancement KW - Optical tweezers KW - Brownian motion KW - Nanoparticles PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-603551 DO - https://doi.org/10.1021/acs.nanolett.4c00379 VL - 24 IS - 12 SP - 3785 EP - 3792 PB - American Chemical Society (ACS) AN - OPUS4-60355 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Dmitriev, A.I. A1 - Gradt, Thomas A1 - Häusler, Ines A1 - Hammouri, Basem A1 - Morales Guzman, Pablo Israel A1 - Wetzel, B. A1 - Yigit, D. A1 - Zhang, G. T1 - Exploring the beneficial role of tribofilms formed from an epoxy-based hybrid nanocomposite N2 - The composition and nanostructure of a beneficial tribofilm formed during sliding of a hybrid nanocomposite against steel were characterized comprehensively. A similar nanostructure was produced by high energy ball milling of the three identified tribofilm constituents: silica, hematite and graphite. By supplying powders to a pin-on-disc test it has been shown that neither silica, nor hematite, nor a mixture of both provide the low coefficient of friction (COF) observed for the hybrid composite. Only if graphite was blended with the oxides, the low COF was obtained. Thus, a film of finely dispersed stable inorganic wear products containing 15 vol% graphite provides low friction and wear in the considered case. KW - TEM KW - Nanocomposite KW - Tribofilm KW - Ball milling KW - Pin-on-disc test PY - 2015 DO - https://doi.org/10.1016/j.triboint.2015.03.006 SN - 0301-679X VL - 88 SP - 126 EP - 134 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-33035 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe A1 - Ainsworth, R. A. A1 - Beier, H.T. A1 - Pisarski, H. A1 - Zhang, Z. L. A1 - Nikbin, K. A1 - Nitschke-Pagel, T. A1 - Münstermann, S. A1 - Kucharczyk, P. A1 - Klingbeil, Dietmar T1 - Review on fracture and crack propagation in weldments - A fracture mechanics perspective N2 - Welding is one of the most common methods in industrial practice for joining components. Its main advantages are high speed in manufacturing combined with low costs and, usually, a high degree of flexibility, integrity and reliability. Nevertheless, welding is a highly complex metallurgical process and, therefore, weldments are susceptible to material discontinuities, flaws and residual stresses which may lead to structural failure and life time reduction. As a consequence weldments are an important field of fracture mechanics methods although its application is more complex than for homogeneous or non-welded structures. The aim of the paper is to provide an overview on the current state of fracture mechanics application to weldments. It starts by discussing the specific features which any fracture mechanics analysis of weldments has to take into account. Then, the experimental determination of fracture toughness, fatigue crack propagation and tensile properties of weldments is addressed. Finally, the analytical determination of the crack driving force in components and structural integrity assessment approaches for weldments are presented. KW - Weldments KW - Fracture mechanics KW - Fracture toughness KW - Fatigue crack propagation KW - Residual stresses KW - Strength mismatch PY - 2014 DO - https://doi.org/10.1016/j.engfracmech.2014.05.012 SN - 0013-7944 SN - 1873-7315 VL - 132 SP - 200 EP - 276 PB - Elsevier Science CY - Kidlington AN - OPUS4-32819 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Na, S.-J. A1 - Han, S.-W. A1 - Muhammad, S. A1 - Zhang, L. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael A1 - Karhu, M. A1 - Kujanpa, V. T1 - Flow and Bead Formation Characteristics in High Power Laser Welding at Different Welding Positions (Invited Talk) N2 - The numerical simulations of high power laser keyhole welding at different welding positions are performed by using Volume-Of-Fluid (VOF) method. The main material is SS400. The multi-physics phenomenon is considered using several models, such as the heat flux of Gaussian heat source, the recoil pressure with Clausisus-Clapeyron equation, the Marangoni flow considering temperature gradient, the buoyancy force with Boussinesq approximation, the additional shear stress and heat source due to metallic vapor ejected through keyhole entrance, the bubble formation assumed as adiabatic bubble, and the multiple-reflection by solving proper discriminant, are used. To analyze the fluid flow pattern, the concept of streamline formed by reconstructing the value of the velocity vector is applied. Partial and full penetration cases at different welding positions are considered. The welding position seems to have only a minor influence on bead formation characteristics in both cases. This is probably due to the fact that the recoil pressure has a major influence when compared to other driving forces. The flow characteristics and fluid velocity in weld pool are analyzed to compare the gravity direction effect at different welding positions. It is observed that the clockwise flow pattern is mainly formed by the recoil pressure on the keyhole surface in the case of partial penetration. The laser energy can't maintain the whole weld pool when the weld pool size becomes too large. And then the solidification starts from the middle part of weld pool and a necked weld pool shape is formed. In the full penetration welding, the weld pool flow patterns are affected by the leakage of laser power through the full penetration keyhole and also by surface tension. Furthermore, the numerical simulation of full penetration welding with AISI316L is also performed to analyze the effect of material properties. The weld bead shapes obtained by simulations were compared with the corresponding experimental results to confirm the validity of the process models adopted and the CFD simulation tool. T2 - Lasers in Manufacturing Conference 2015 CY - München, Germany DA - 22.06.2015 KW - Macro Processing (Joining, Welding) KW - Weld pool KW - Flow pattern KW - Different welding position KW - Numerical simulation KW - High power laser keyhole welding PY - 2015 SP - 1 EP - 6 AN - OPUS4-37163 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, G. A1 - Österle, Werner A1 - Jim, B. A1 - Häusler, Ines A1 - Hesse, Rene A1 - Wetzel, B. T1 - The role of surface topography in the evolving microstructure and functionality of tribofilms of an epoxy-based nanocomposite N2 - The topographic effect of steel counterface, finished by mechanical grinding with Ra ranging from 0.01 to 0.95 µm, on the structure and functionality of the tribofilm of a hybrid nanocomposite, i.e. epoxy matrix filled with monodisperse silica nanoparticles, carbon fibers and graphite, was systematically investigated. The nanostructure of the tribofilm was comprehensively characterized by using combined focused ion beam and transmission electron microscope analyses. It was identified that oxidation of the steel surface, release, compaction and tribosintering of silica nanoparticles and deposition of an epoxy-like degradation product as well as fragmentation of carbon fibers are main mechanisms determining the structure and functionality of the tribofilm. The size of roughness grooves determines the type and size class of wear particles to be trapped at the surface. An optimum groove size leading to a maximum of surface coverage with a nanostructured tribofilm formed mainly from released silica nanoparticles was identified. KW - hybrid nanocomposite KW - tribological performance KW - topographic effect KW - tribofilm KW - nanostructure PY - 2016 DO - https://doi.org/10.1016/j.wear.2016.06.012 VL - 364-365 SP - 48 EP - 56 PB - Elsevier B.V. AN - OPUS4-37937 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dmitriev, A.I. A1 - Österle, Werner A1 - Wetzel, B. A1 - Zhang, G. T1 - Mesoscale modeling of the mechanical and tribological behavior of a polymer matrix composite based on epoxy and 6 vol.% silica nanoparticles N2 - A model based on movable cellular automata (MCA) is described and applied for simulating the stress–strain and sliding behavior of a nanocomposite consisting of an epoxy matrix and 6 vol.% of homogeneously distributed silica nanoparticles. Tensile tests were used for verification of the model. It was realized that a slight modification of epoxy properties due to the addition of silica nanoparticles had to be taken into account in order to obtain good correlation between experimental and modeling results. On the other hand, sliding simulations revealed no susceptibility of results to slight modifications of matrix properties, but a significant impact of nanoparticles on the interface structure and smoothness of sliding mechanism. Furthermore, assuming both possibilities, bond breaking and rebinding of automata pairs, can explain different friction levels of polymer materials. KW - Nanocomposite KW - Stress–strain behavior KW - Movable cellular automata KW - Sliding simulation KW - Mechanically mixed layer KW - Coefficient of friction PY - 2015 DO - https://doi.org/10.1016/j.commatsci.2015.08.029 SN - 0927-0256 VL - 110 SP - 204 EP - 214 PB - Elsevier CY - Amsterdam AN - OPUS4-34013 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, G. A1 - Häusler, Ines A1 - Österle, Werner A1 - Wetzel, B. A1 - Jim, B. T1 - Formation and function mechanisms of nanostructured tribofilms of epoxy-based hybrid nanocomposites N2 - The nanostructures and properties of the tribofilms of epoxy (EP) composites filled with short carbon fibers (SCF) and different volume fractions of monodisperse silica nanoparticles were investigated. When the conventional composite filled only with SCF was considered under a high pv condition, an iron oxide layer is formed on the steel counterface. The addition of even only 0.05 vol% nano-silica leads to a significant change of the tribofilm's structure and the tribological behavior of the composite. With increasing silica content, the oxidation layer on the steel surface is gradually replaced by a silica-based tribofilm. A close relationship between the tribofilms’ structure and the tribological behavior of the composites was identified. Mixing, possible reactions and tribo-sintering of silica nanoparticles with other wear products are deemed to be main mechanisms inducing the formation and the lubricity of the silica-based tribofilm. KW - Polymer-matrix composite KW - Sliding wear KW - Tribofilm KW - Nanoparticles KW - Tribo-sintering PY - 2015 DO - https://doi.org/10.1016/j.wear.2015.08.025 SN - 0043-1648 VL - 342-343 SP - 181 EP - 188 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-34442 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zhang, Lei T1 - Applications of Thermo-Calc in Weld Metallurgy T2 - Thermo-Calc Anwendertreffen CY - Aachen, Germany DA - 2015-09-03 PY - 2015 AN - OPUS4-34398 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Griesche, Axel A1 - Zhang, B. A1 - Solórzano, E. A1 - Garcia-Moreno, F. T1 - Note: X-ray radiography for measuring chemical diffusion in metallic melts N2 - A x-ray radioscopy technique for measuring in situ chemical diffusion coefficients in metallic melts is presented. The long-capillary diffusion measurement method is combined with imaging techniques using microfocus tubes and flat panel detectors in order to visualize and quantitatively analyze diffusive mixing of two melts of different chemical composition. The interdiffusion coefficient as function of temperature and time is obtained by applying Fick’s diffusion laws. Tracking the time dependence of the mean square penetration depth of the mixing process allows to detect changes in the mass transport caused by convective flow. The possibility to sort out convective mass transport contributions from analysis enhances significantly the accuracy compared to the conventional long-capillary diffusion measurement method with postmortem analysis. The performance of this novel diffusion measurement method with x-ray radiography technique is demonstrated by a diffusion experiment in an Al-Ni melt. KW - Diffusion KW - Metal KW - Aluminium KW - Nickel KW - Melt KW - In-situ KW - Radiography KW - Capillary KW - Aluminium-alloys KW - Chemical analysis KW - Chemical interdiffusion KW - Convection KW - Liquid alloys KW - Mass transfer KW - Nickel alloys KW - X-ray apparatus PY - 2010 DO - https://doi.org/10.1063/1.3427256 SN - 0034-6748 SN - 1089-7623 VL - 81 SP - 056104-1 - 056104-3 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21333 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -