TY - JOUR A1 - Wu, W. A1 - Wei, A. A1 - Huang, W. A1 - Zhao, Peng A1 - Schmidt, Martin A1 - Krause, Ulrich A1 - Wu, Dejian T1 - Experimental and theoretical study on the inhibition effect of CO2/N2 blends on the ignition behavior of carbonaceous dust clouds N2 - Gaseous inhibitors are used in many industries for the explosion prevention of combustible dusts, mitigating the potential hazard to humans, properties and environments. This work experimentally and theoretically studied the inerting effect of gaseous inhibitors on the ignition process of dust clouds in O2/N2/CO2 atmospheres, with an emphasis on the role of the CO2/N2 ratio. 10 different combustible carbonaceous dusts were selected, including grain dust, biomass dust and coal dust. Experimental results showed that the inhibition effect of CO2/N2 is closely related to the ignition mechanism of dust clouds. Specifically, a higher ratio of CO2/N2 yields a stronger inhibition effect on the ignition process of dust samples with relatively low volatile matter contents predominated by heterogeneous ignition. In addition, two novel steady-state ignition mechanism models were developed to interpret the experimental observations. Maxwell-Stefan equations were used to describe the diffusivity in the ternary O2/N2/CO2 gas mixtures. The analytical results were in good agreement with the experimental data of the minimum ignition temperature of dust cloud (MITC) in oxygen-lean atmospheres. The mechanism modelling can be used to estimate the critical ignition temperature of all carbonaceous dust clouds with a wide range of volatile matter content under different inert atmospheres, which will provide a reference for the explosion hazard assessment of dust posed by a hot surface in the process industries. KW - CO2/N2 ratio KW - Inerting effect KW - Volatile matter content KW - MITC KW - Mechanism model PY - 2021 DO - https://doi.org/10.1016/j.psep.2021.07.005 SN - 0957-5820 VL - 153 SP - 1 EP - 10 PB - Elsevier B.V. AN - OPUS4-53662 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wu, Dejian A1 - Schmidt, Martin A1 - Huang, W. A1 - Wei, A. A1 - Krause, U. A1 - Wu, W. T1 - Inhibition effect of N2/CO2 blends on the minimum explosion concentration of agriculture and coal dusts N2 - Minimum explosion concentration (MEC) of three agriculture dusts and two coal dusts was studied via a 20-L explosion chamber to reveal the role of gaseous inhibitors. Both active method (CO2 diluting air) and passive method (CO2 replacing O2) were used. The TG and DTG thermal analysis tests were conducted to study the pyrolysis and combustion characteristics of dust samples. An alternative explosion criterion based on combustion duration time was used to determine MEC, and compared with the standardized overpressure method. Under 10-kJ ignition condition, as oxygen mole fraction (XO2) decreased from 21% to 10%, MEC of agriculture dusts and coal dusts respectively increased by around 5 times and 2 times. The active inerting method with a lower N2/CO2 ratio was found to have a better suppression effect on the explosion of the five carbonaceous dusts because the blend has a higher specific heat and a lower oxygen diffusion rate. KW - CO2/N2 ratio KW - Explosion criterion KW - Combustion kinetics KW - Inerting effect KW - Explosion characteristics PY - 2022 DO - https://doi.org/10.1016/j.powtec.2022.117195 SN - 0032-5910 VL - 399 SP - 1 EP - 12 PB - Elsevier B.V. AN - OPUS4-55013 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yildirim, Arda A1 - Krause, Christina A1 - Zorn, R. A1 - Lohstroh, W. A1 - Schneider, G. J. A1 - Zamponi, M. A1 - Holerer, O. A1 - Frick, B. A1 - Schönhals, Andreas T1 - Complex molecular dynamics of a symmetric model discotic liquid crystal revealed by broadband dielectric, thermal and neutron spectroscopy N2 - The molecular dynamics of the triphenylene-based discotic liquid crystal HAT6 is investigated by broadband dielectric spectroscopy, advanced dynamical calorimetry and neutron scattering. Differential scanning calorimetry in combination with X-ray scattering reveals that HAT6 has a plastic crystalline phase at low temperatures, a hexagonally ordered liquid crystalline phase at higher temperatures and undergoes a clearing transition at even higher temperatures. The dielectric spectra show several relaxation processes: a localized gamma-relaxation a lower temperature and a so called alpha-2-relaxation at higher temperatures. The relaxation rates of the alpha-2-relaxation have a complex temperature dependence and bear similarities to a dynamic glass transition. The relaxation rates estimated by hyper DSC, Fast Scanning calorimetry and AC Chip calorimetry have a different temperature dependence than the dielectric alpha-2-relaxation and follows the VFT-behavior characteristic for glassy dynamics. Therefore, this process is called alpha-1-relaxation. Its relaxation rates show a similarity with that of polyethylene. For this reason, the alpha-1-relaxation is assigned to the dynamic glass transition of the alkyl chains in the intercolumnar space. Moreover, this process is not observed by dielectric spectroscopy which supports its assignment. The alpha-2-relaxation was assigned to small scale translatorial and/or small angle fluctuations of the cores. The neutron scattering data reveal two relaxation processes. The process observed at shorter relaxation times is assigned to the methyl group rotation. The second relaxation process at longer time scales agree in the temperature dependence of its relaxation rates with that of the dielectric gamma-relaxation. KW - Discotic Liquid Crystals PY - 2020 DO - https://doi.org/10.1039/c9sm02487e VL - 16 IS - 8 SP - 2005 EP - 2016 PB - Royal Chemical Society AN - OPUS4-50466 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Algernon, A. A1 - Walther, A. A1 - Denzel, W. A1 - Ebsen, B. A1 - Feistkorn, S. A1 - Friese, M. A1 - Grosse, C. A1 - Kathage, S. A1 - Kessler, S. A1 - Köpp, Christian A1 - Krause, M. A1 - Maack, Stefan A1 - Schickert, M. A1 - Taffe, A. A1 - Timofeev, Juri A1 - Wilcke, M. A1 - Wolf, J. T1 - Qualitätssicherung und Validierung der Anwendung zerstörungsfreier Prüfungen von Stahlbetonbauteilen im Bauwesen N2 - Stahlbetontragwerke sind eine wichtige Konstruktionsweise im Bauwesen und ein wachsendes Anwendungsfeld für die Zerstörungsfreie Prüfung (ZfP). Zur Sicherung der Tragsicherheit, strukturellen Integrität, Bestimmung von Geometrien und zur Detektion konstruktiver Elemente wie z.B. Bewehrung, Verankerungen und Spannkanälen besitzen zerstörungsfreie Prüfverfahren in diesem Bereich inzwischen große Relevanz. Durch den bislang erreichten Fortschritt in der Forschung und Entwicklung haben moderne akustische und elektromagnetische Verfahren eine beachtliche Leistungsfähigkeit erreicht. Von Geräteherstellern sind diese in kommerziellen Produktserien umgesetzt worden und finden eine zunehmend breite Anwendung in der Praxis. In einigen anderen Anwendungsgebieten, in denen die ZfP bereits fester Bestandteil von Überwachungen ist, wie z.B. im Maschinenbau und insbesondere in der Kerntechnik und der Luftfahrt, existieren umfangreiche Qualitätssicherungssysteme für die konforme Anwendung und zuverlässige Einbeziehung der ZfP. Dem relativ jungen Entwicklungsstadium moderner ZfP für Stahlbetonbauteile entsprechend müssen solche Konzepte im Bauwesen erst noch entwickelt bzw. implementiert werden. Dementsprechend hat sich der Unterausschuss Qualitätssicherung (UA- S) des Fachausschusses ZfP im Bauwesen (ZfPBau) die Definition und Verbesserung der Qualität von ZfP-Anwendungen sowie insbesondere die verfahrensunabhängige Standardisierung von Prüfprozeduren und statistische Absicherung der Prüfergebnisse zum Ziel gemacht. Die aktuellen Arbeitsfelder beinhalten die Entwicklung praxisgerechter Konzepte für Prüfprozeduren und deren Erprobung in einem Ringversuch sowie die Konzeption von Testkörpern hinsichtlich unterschiedlicher Aspekte wie Parameterstudien, Validierung, Kalibrierung und Simulation. Dabei werden Ansätze anderer Branchen durchaus einbezogen, die Anpassung an die spezifischen Bedürfnisse und Gegebenheiten des Bauwesens wird jedoch als wesentlich angesehen und stellt somit eine wichtige Vorgabe dar. Da die Tätigkeiten nicht auf einzelne Verfahren begrenzt sind, müssen generelle Vorgehensweisen entwickelt werden, die sich auf die jeweiligen Verfahren konkretisieren lassen. Der Vortrag gibt hierzu erste Einblicke in die Arbeit des Ausschusses. T2 - DGZfP-Jahrestagung 2018 CY - Leipzig, Germany DA - 07.05.2018 KW - Zerstörungsfreie Prüfung KW - Beton KW - Qualitätssicherung KW - Validierung PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-472417 SP - 1 EP - 9 AN - OPUS4-47241 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Streicher, Doreen A1 - Krause, Martin A1 - Kohl, Christoph A1 - Schickert, M. A1 - Kroggel, O. A1 - Müller, W. T1 - Parameters for the Quantitative Assessment of Ulrasonic Imaging for Concrete Elements N2 - Ultrasonic investigation is an established non-destructive testing method for detection of defects and material characterisation. In the last years scanning ultrasonic echo methods were developed especially for the application in civil engineering. The different scanning ultrasonic echo methods are modified with respect to the type of the transducer applied, the number and the arrangement of transducers and the frequency used. Also different algorithms are used to analyse the measured data, for instance SAFT (Synthetic Aperture Focusing Technique) reconstruction. The results are typically presented as B- and C-scans, obtained from raw data or the SAFT reconstructed data. Since 2001 several German research institutes co-operate within the scope of the research initiative Non-destructive Evaluation of Concrete Structures Using Acoustic and Electromagnetic Echo-Methods (FOR 384) supported by the Deutsche Forschungsgemeinschaft (DFG). One of the tasks is to investigate these ultrasonic echo methods for special applications like the detection of cavities in concrete structures or faults in tendon ducts. Concrete test specimens with intentional faults have been manufactured and investigated. Parameters were defined to assess the results more objectively. Currently three parameters -signal/noise-ratio, lateral edge resolution and uniformity- are considered. For the first time results of different working groups on the same imaged objects are compared quantitatively. It should help to get more knowledge about the ultrasonic inspection of typical faults in civil engineering structures. T2 - 6th International Symposium Non-Destructive Testing in Civil Engineering (NDT-CE) CY - Berlin, Germany DA - 2003-09-16 PY - 2003 UR - http://www.ndt.net/article/ndtce03/papers/p050/p050.htm SN - 3-931381-49-8 SP - 1(?) EP - 12(?) PB - DGZfP CY - Berlin AN - OPUS4-2751 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schickert, M. A1 - Krause, Martin A1 - Müller, W. T1 - Ultrasonic Imaging of Concrete Elements Using Reconstruction by Synthetic Aperture Focusing Technique N2 - Ultrasonic reconstruction by the synthetic aperture focusing technique (SAFT) has a great potential to image concrete elements and detect embedded objects. Its algorithm focuses ultrasonic signals received at many aperture points by coherent superposition, yielding a high-resolution image of the region of interest. Using this approach, several problems caused by the strongly inhomogeneous structure of concrete are diminished, where scattering of transmitted pulses leads to disturbing phenomena such as attenuation and structural noise. This contribution is intended to review the work of the writers on the application of SAFT reconstruction to concrete testing. First, consequences of scattering of ultrasonic waves in concrete are qualitatively explained. Then the use of SAFT is discussed in comparison to traditional A-scan and B-scan techniques. Different reconstruction algorithms and implementations are presented for one-, two-, and three-dimensional SAFT. Pulse-echo measurement systems are described, which are able to acquire large sets of data on linear and planar apertures employing single transducer, transducer array, and scanning laser Doppler vibrometer arrangements. To illustrate the application of the SAFT techniques, examples from laboratory and field experiments are described comprising imaging of back walls, tendon ducts containing faults, layers, and reinforcement in concrete elements. KW - Imaging techniques KW - Concrete KW - Acoustic detection PY - 2003 DO - https://doi.org/10.1061/(ASCE)0899-1561(2003)15:3(235) SN - 0899-1561 SN - 1943-5533 IS - May/June SP - 235 EP - 246 PB - American Society of Civil Engineers CY - New York, NY AN - OPUS4-2752 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Moritz, W. A1 - Krause, S. A1 - Roth, U. A1 - Klimm, D. A1 - Lippitz, Andreas T1 - Re-activation of an all solid state oxygen sensor N2 - The silicon based semiconductor structure Si/SiO2/Si3N4/LaF3/Pt can be used as a potentiometric oxygen sensor working at room temperature. A thermal re-activation can be applied to overcome the earlier disadvantage of an increase in response time with continuous use. Using the Pt gate electrode as a resistive heater, very short electrical high-power pulses can be applied. A heating time as short as 300 ns was sufficient for the re-activation of the sensor. This way, only the sensitive thin layer system LaF3/Pt was heated, and the whole sensor was at room temperature immediately after heating. Impedance spectroscopy, X-ray photoelectron spectroscopy (XPS) and quadruple mass spectrometric (QMS)–thermogravimetry (TG) were used to investigate the mechanism of deterioration in dynamic sensor behaviour and re-activation. The formation of hydrated carbonate and the desorption of CO2 and H2O have been shown to be the causes. KW - Chemical sensor KW - Thermal treatment KW - Activation KW - LaF3 KW - Pt PY - 2001 DO - https://doi.org/10.1016/S0003-2670(01)00993-X SN - 0003-2670 SN - 1873-4324 SN - 0378-4304 VL - 437 SP - 183 EP - 190 PB - Elsevier CY - Amsterdam AN - OPUS4-6836 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Krause, Martin A1 - Mielentz, Frank A1 - Milmann, Boris A1 - Streicher, Doreen A1 - Müller, W. T1 - Ultrasonic Imaging of Concrete Elements - State of the Art Using 2D Synthetic Aperture N2 - Since several years ultrasonic imaging techniques are used for testing concrete elements. Combined with a reconstruction calculation they lead to an acoustic imaging of scatterers and reflectors from the inside of the concrete element. For several testing problems it is an advantage to use a two dimensional synthetic aperture and to combine it with a three-dimensional reconstruction calculation (3D-SAFT, Synthetic Aperture Focussing Technique). This enables the analysis of the tested volume by means of B-scans in two directions and C-scans (projections parallel to the surface), respectively. Using the 2D-scanning technique, especially the disturbing influence of the reinforcing rebars can be minimised. In this contribution the state of the art of this method is demonstrated and analysed. Examples of the application are presented, concerning Localisation of honeycombing and compaction faults Characterisation of cracks (especially measuring the crack depth) Investigation of tendon ducts The results presented are obtained in the frame of a research initiative Non-destructive Evaluation of Concrete Structures Using Acoustic and Electromagnetic Echo-Methods supported by the German Science Council (FOR 384 of DFG, Deutsche Forschungsgemeinschaft). The methods are assessed and improved in cooperation with the partners participating in the project. T2 - 6th International Symposium Non-Destructive Testing in Civil Engineering (NDT-CE) CY - Berlin, Germany DA - 2003-09-16 PY - 2003 UR - http://www.ndt.net/article/ndtce03/papers/v051/v051.htm SN - 3-931381-49-8 PB - DGZfP CY - Berlin AN - OPUS4-2606 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Hasenstab, Andreas A1 - Krause, Martin A1 - Hillger, w. A1 - Bühling, L. A1 - Ilse, D. A1 - Hillemeier, B. A1 - Rieck, C. T1 - Luftultraschall und Ultraschall-Echo-Technik an Holz T2 - DGZfP Jahrestagung CY - Rostock, Deutschland DA - 2005-05-02 KW - ZfP an Holzbauteilen KW - Fehlstellen KW - Minderdicken KW - Ultraschallecho-Experimente an Probekörpern KW - Ultraschall-Echo KW - Fäulnis KW - Bauwesen KW - Luftultraschall PY - 2005 SN - 3-931381-64-1 N1 - Serientitel: Berichtsband / Deutsche Gesellschaft für zerstörungsfreie Prüfung e. V. – Series title: Berichtsband / Deutsche Gesellschaft für zerstörungsfreie Prüfung e. V. IS - 94-CD SP - 1(?) EP - 15(?) PB - DGZfP CY - Berlin AN - OPUS4-11961 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Mielentz, Frank A1 - Milmann, Boris A1 - Wöstmann, Jens A1 - Krause, Martin A1 - Maierhofer, Christiane A1 - Römer, A. A1 - Völkel, W. T1 - Untersuchungen zur zerstörungsfreien Bestimmung des Hohlraumgehaltes von Asphaltschichten T2 - DGZfP-Fachtagung Bauwerksdiagnose "Praktische Anwendungen Zerstörungsfreier Prüfungen" CY - Berlin, Deutschland DA - 2006-02-22 KW - Asphalt KW - Hohlraumgehalt KW - Zerstörungsfreie Prüfung KW - Ultraschallverfahren KW - Ultraschall-Rückstreuung KW - Radarverfahren PY - 2006 SN - 3-931381-71-4 SP - 1(?) EP - 9(?) PB - DGZfP CY - Berlin AN - OPUS4-12116 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -