Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (27)
- Beitrag zu einem Tagungsband (6)
- Forschungsbericht (3)
- Beitrag zu einem Sammelband (2)
- Monografie (1)
- Buchkapitel (1)
Schlagworte
- Cement (5)
- Concrete (4)
- Dust explosions (3)
- Gas explosions (3)
- Hybrid mixtures (3)
- Africa (2)
- Analysis (2)
- CO2/N2 ratio (2)
- Dye (2)
- Fluorescence (2)
Organisationseinheit der BAM
- 2 Prozess- und Anlagensicherheit (6)
- 2.1 Sicherheit von Energieträgern (6)
- 1 Analytische Chemie; Referenzmaterialien (4)
- 1.2 Biophotonik (2)
- 7 Bauwerkssicherheit (2)
- 7.4 Baustofftechnologie (2)
- 1.0 Abteilungsleitung und andere (1)
- 1.4 Prozessanalytik (1)
- 6 Materialchemie (1)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (1)
An international interlaboratory comparison of the measurement capabilities of four National Metrology Institutes (NMIs) and one Designated Institute (DI) in the determination of the chemical composition of thin Fe-Ni alloy films was conducted via a key comparison (K-67) of the Surface Analysis Working Group of the Consultative Committee for Amount of Substance. This comparison was made using XPS (four laboratories) and AES (one laboratory) measurements. The uncertainty budget of the measured chemical composition of a thin alloy film was dominated by the uncertainty of the certified composition of a reference specimen which had been determined by inductively coupled plasma mass spectrometry using the isotope dilution method. Pilot study P-98 showed that the quantification using relative sensitivity factors (RSFs) of Fe and Ni derived from an alloy reference sample results in much more accurate result in comparison to an approach using RSFs derived from pure Fe and Ni films. The individual expanded uncertainties of the participants in the K-67 comparison were found to be between 2.88 and 3.40 atomic %. The uncertainty of the key comparison reference value (KCRV) calculated from individual standard deviations and a coverage factor (k) of 2 was 1.23 atomic %.
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.
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.
This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries.
The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.
Fe-ZSM-5 Catalysts for the Selective Reduction of NO by Isobutane - The Problem of the Active Sites
(2002)
Relations between the structure of FeZSM-5 catalysts prepared by interaction of FeCl3 with HZSM-5 and their catalytic behavior in the SCR of NO by isobutane were investigated by combining results of catalytic studies (1000 ppm NO, 1000 ppm isobutane, and 2% O2 in He, 30,000 h-1) and of physicochemical characterization (XRD, EXAFS, Mössbauer spectroscopy, TPR, IR, XPS). By variation of the preparation conditions (method of FeCl3 introductionchemical vapor deposition or solid-state ion exchange, washing intensity, calcination regime) and of the matrix (HZSM-5 with normal and high defect density), FeZSM-5 materials with strongly varying properties (aggregation degree of the Fe phase, acidity) were obtained. Significant discrepancies between conclusions derived from EXAFS, TPR, and Mössbauer spectroscopy were ascribed to a preference of Mössbauer spectroscopy for the detection of aggregated phases and a high defectivity of Fe oxide clusters formed upon calcination. The critical step for the preparation of a highly disperse Fe phase is extensive washing after Fe introduction. The catalytic behavior of overexchanged FeZSM-5 materials prepared by interaction of FeCl3 with HZSM-5 of normal defect density was not influenced by aggregation of a significant part of the Fe phase. The comparison of their catalytic properties with those of a Fe2O3/HZSM-5 mechanical mixture and of catalysts prepared by aqueous ion exchange or by CVD of FeCl3 into HZSM-5 of high defect density implies that the particular activity of overexchanged FeZSM-5 arises from minority sites. In these, the Fe ions are probably isolated. Other Fe sites of low nuclearity appear to add to the activity. The poor SCR performance (at a given ability for isobutane activation) of FeZSM-5 prepared with a defective ZSM-5 matrix may indicate that the Fe sites which provi de the particular activity of overexchanged FeZSM-5 require the cooperation of acidic sites.
Nanotechnologien werden gegenwärtig als leistungsfähige Oberflächentechniken in erheblichem Umfange industriell genutzt. Dabei spielen dünne Schichten und deren Kenndaten eine wesentliche Rolle, z.B. als Röntgenspiegel oder optische und magnetooptische Datenträger. Die Schichtdicke zählt hierbei zu den technologisch wichtigen Parametern. Abgeleitet von Anwenderinteressen, werden für die Röntgenreflektometrie (XRR bzw. GIXR), Elektronenstrahl-Mikroanalyse (EPMA) und Röntgenfluoreszenzanalyse (XRF) einerseits und die Ellipsometrie andererseits zugeschnittene Schichtdickenmaßverkörperungen (SDM) entwickelt, gefertigt und untersucht. Das Ziel ist die Bereitstellung praxistauglicher, kalibrierter SDM, im weiteren Schichtdickennormale (SDN) genannt. SDN sind Maßverkörperungen, für die der Schichtdickenwert mit einer definierten Messunsicherheit bekannt und auf ein metrologisch anerkanntes Längennormal zurückgeführt ist. Berichtet wird über die Herstellung und messtechnische Charakterisierung der beiden spezifischen Varianten von Maßverkörperungen.
Studienziel: Zwei Nagelsysteme, zum einen der unaufgebohrte Tibianagel mit 3fach-Verriegelung in 2 Ebenen und großem Bolzenspiel (UTN® der Fa. Mathys®) mit der Möglichkeit von medial zweifach und von ventral einfach zu verriegeln und zum anderen der unaufgebohrte Tibianagel mit 3fach-Verriegelung in einer Ebene mit geringem Bolzenspiel (Targon®-Nagel der Fa. Aesculap®), der 3 mediale Verriegelungsmöglichkeiten besitzt, wurden im Biegeversuch statisch geprüft. Anatomisch besteht bei der ventralen Verriegelung immer die Verletzungsmöglichkeit von Sehnen, Nerven und Gefäßen. Andererseits besteht bei einem höheren Bolzenspiel immer ein höherer Instabilitätsgrad. Inwieweit ist die Verriegelung in zwei Ebenen notwendig?
Methode: Wir prüften statisch zwei intramedulläre Verriegelungssysteme an 8 Leichenknochen (matched pairs) in zwei Ebenen an einer Universalprüfmaschine der Firma Schenk-Trebel im Biegeversuch.
Ergebnisse: Die Untersuchungsergebnisse zeigen, dass nicht die Bolzenlage, sondern das so genannte Bolzenspiel für die Stabilität der distalen Fragmente entscheidend ist. Die Verriegelung sollte somit prinzipiell durch ein formschlüssiges winkelstabiles Bolzensystem möglich sein.
Innovative Technologien für die Erkundung, Löschung und Beobachtung von Kohlebränden - Phase B -
(2011)
Aufbauend auf den Erkenntnissen der Phase A, die sich auf das grundlegende Verständnis von Kohlebränden, sowie der Voraussetzung und des prinzipiellen Ablaufs der physikalischchemischen Brandprozesse konzentriert haben, erfolgte in Phase B eine Fokussierung auf Methoden zur Vermeidung von Kohlebränden, sowie der Löschung und Überwachung von Kohlebrandzonen, um einen Beitrag zur Verminderung von C02-Emissionen und zum Erhalt der nutzbaren Energieressourcen leisten zu können. Diese Arbeiten erfolgten insbesondere mit Bezug zu den „Clean Development Mechanisms“ (CDM), die im Rahmen des Kyoto-Protokolls entwickelt worden sind.
Eine Zertifizierung von Löschaktivitäten im Rahmen des Kyoto-Protokolls setzt dabei eine nachvollziehbare Ermittlung der kohlebrandbezogenen C02-Emissionen und eine belastbare Abschätzung der durch die Löschung verringerten Emissionsmengen voraus. Wesentliche Arbeiten konzentrierten sich auf die Entwicklung von Verfahren, die eine solche Abschätzung gewährleisten können. Dazu wurden unterschiedliche Ansätze entwickelt und anhand der erhobenen Felddaten überprüft. Die untersuchten Ansätze konzentrierten sich dabei auf Verfahren, die eine Ermittlung des vorhandenen Kohlevolumens, die Erfassung der emittierten Gase und die durch die Kohlebrände verursachten Temperaturanomalien an der Tagesoberfläche ermöglichen. Die direkten Arbeiten zum Thema CDM wurden dabei in einem Arbeitspaket unter Federführung der BGR gebündelt.
Die deutsche Initiative zur Erforschung der Kohlenbrände in der V.R. China leistete zweifelsfrei signifikante Beiträge zu den oben genannten Zielen. Durch die inventiven Ansätze im Bereich der Brandbewältigung konnte darüber hinaus auch in Teilen die ökonomischen Chancen für ein Engagement deutscher Unternehmen aufgezeigt werden.
Uncontrolled burning or smoldering of coal seams, otherwise known as coal fires, represents a worldwide natural hazard. Efficient application of fire-fighting strategies and prevention of mining hazards require that the temporal evolution of fire propagation can be sufficiently precise predicted. A promising approach for the investigation of the temporal evolution is the numerical simulation of involved physical and chemical processes.
In the context of the Sino-German Research Initiative Innovative Technologies for Detection, Extinction and Prevention of Coal Fires in North China, a numerical model has been developed for simulating underground coal fires at large scales. The objective of such modelling is to investigate observables, like the fire propagation rate, with respect to the thermal and hydraulic parameters of adjacent rock. In the model, hydraulic, thermal and chemical processes are accounted for, with the last process complemented by laboratory experiments.
Numerically, one key challenge in modelling coal fires is to circumvent the small time steps resulting from the resolution of fast reaction kinetics at high temperatures. In our model, this problem is solved by means of an operator-splitting approach, in which transport and reactive processes of oxygen are independently calculated. At high temperatures, operator-splitting has the decisive advantage of allowing the global time step to be chosen according to oxygen transport, so that time-consuming simulation through the calculation of fast reaction kinetics is avoided. Also in this model, because oxygen distribution within a coal fire has been shown to remain constant over long periods, an additional extrapolation algorithm for the coal concentration has been applied.
In this paper, we demonstrate that the operator-splitting approach is particularly suitable for investigating the influence of hydraulic parameters of adjacent rocks on coal fire propagation. A study shows that dynamic propagation strongly depends on permeability variations. For the assumed model, no fire exists for permeabilities k < 10-10 m2, whereas the fire propagation velocity ranges between 340 m a-1 for k = 10-8 m2, and drops to lower than 3 m a-1 for k = 5 × 10-10 m2. Additionally, strong temperature variations are observed for the permeability range 5 × 10-10 m2 < k < 10-8 m2.
High-accuracy film thickness measurements in the range below 100 nm can be made by various complex methods like spectral ellipsometry (SE), scanning force microscopy (SFM), grazing incidence X-ray reflectometry (GIXR), or X-ray fluorescence analysis (XRF). The measurement results achieved with these methods are based on different interactions between the film and the probe. A key question in nanotechnology is how to achieve consistent results on a level of uncertainty below one nanometre with different techniques.
Two different types of thickness standards are realised. Metal film standards for X-ray techniques in the thickness range 10 to 50 nm are calibrated by GIXR with monochromatised synchrotron radiation of 8048 eV. The results obtained at four different facilities show excellent agreement. SiO2 on Si standards for SE and SFM in the thickness range 6 to 1000 nm are calibrated by GIXR with monochromatised synchrotron radiation of 1841 eV and with a metrological SFM. Consistent results within the combined uncertainties are obtained with the two methods. Surfaces and interfaces of both types of standards are additionally investigated by transmission electron microscopy (TEM).
We present a synchrotron X-ray tomographic study on the morphology of carbon fiber-based gas diffusion layer (GDL) material under compression. A dedicated compression device is used to provide well-defined compression conditions. A flat compression punch is employed to study the fiber geometry at different degrees of compression. Transport relevant geometrical parameters such as porosity, pore size and tortuosity distributions are calculated. The geometric properties notably change upon compression which has direct impact on transport conditions for gas and fluid flow. The availability of broad 3D paths, which are most important for the transport of liquid water from the catalyst layer through the GDL, is markedly reduced after compression. In a second experiment, we study the influence of the channel-land-pattern of the flow-field on shape and microstructure of the GDL. A flow-field compression punch is employed to reproduce the inhomogeneous compression conditions found during fuel cell assembly. While homogenously compressed underneath the land the GDL is much less and inhomogeneously compressed under the channel. The GDL material extends far into the channel volume where it can considerably influence gas and fluid flow. Loose fiber endings penetrate deeply into the channel and form obstacles for the discharge of liquid water droplets.
Minimum ignition temperature of dust clouds (MITC) was studied experimentally and theoretically in different atmospheres. Three carbonaceous dusts were tested in both air and O2/CO2 atmospheres with CH4 mole fraction from 0 to 2%. Results showed that the ignition risk of the three dusts significantly increases (decrease of MITC by ~100 ℃) with increasing XO2 from 21% to 50%, but significantly decreases replacing N2 in air with CO2. The inhibition effect of CO2 on MITCs could be diminished by increasing XO2 or adding CH4. The addition of small amount of CH4 has different effects on the MITCs of different dust samples, following the opposite order of volatile matter content: anthracite>bituminous coal>starch. Two modified steady-state ignition models, considering the density of mixture gas and dust cloud, XO2 and its diffusivity, were developed to interpret the experimental observations. The analysis revealed that the global heterogeneous ignition model suits well for the hybrid mixtures of anthracite or bituminous coal dusts. In contrast, the proposed global homogeneous ignition model was found to be only valid for the pure starch dust, and the extra CH4 addition could strongly affect the ignition process of starch, particularly in O2/CO2 atmospheres with higher XO2.
Carbon fiber based felt materials are widely used as gas diffusion layer (GDL) in fuel cells. Their transport properties can be adjusted by adding hydrophobic agents such as polytetrafluoroethylene (PTFE). We present a synchrotron X-ray tomographic study on the felt material Freudenberg H2315 with different PTFE finishing. In this study, we analyze changes in microstructure and shape of GDLs at increasing degree of compression which are related to their specific PTFE load. A dedicated compression device mimicking the channel-land pattern of the flowfield is used to reproduce the inhomogeneous compression found in a fuel cell. Transport relevant geometrical parameters such as porosity, pore size distribution and geometric tortuosity are calculated and consequences for media transport discussed. PTFE finishing results in a marked change of shape of compressed GDLs: surface is smoothed and the invasion of GDL fibers into the flow field channel strongly mitigated. Furthermore, the PTFE impacts the microstructure of the compressed GDL. The number of available wide transport paths is significantly increased as compared to the untreated material. These changes improve the transport capacity liquid water through the GDL and promote the discharge of liquid water droplets from the cell.