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- Permeation (16) (entfernen)
Organisationseinheit der BAM
- 3 Gefahrgutumschließungen; Energiespeicher (1)
- 3.5 Sicherheit von Gasspeichern (1)
- 6 Materialchemie (1)
- 6.6 Physik und chemische Analytik der Polymere (1)
- 7 Bauwerkssicherheit (1)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (1)
- 8 Zerstörungsfreie Prüfung (1)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (1)
- 9 Komponentensicherheit (1)
- 9.0 Abteilungsleitung und andere (1)
Eingeladener Vortrag
- nein (3)
The subject of permeation of hoses according to ISO 3821 for
hydrogen was discussed for a long time in ISO/TC 44/SC 8. The reason
is a considerable leakage of hydrogen diffused into the hose material
over the end face of the hose. Because of this unsolved, safety-related
problem of hoses sold on the market, measurements should be carried
out in order to be able to better assess the problem. BAM has declared
its attendance to provide a required fast solution to this issue.
Polymeric membranes represent a cost- and energy-efficient solution for gas separation. Recently Polymers of Intrinsic Microporosity (PIMs) have been in a great interest because of their outstanding BET surface area larger than 700m2/g and pore size smaller than 1 nm. PIMs are a promising candidate in gas separation with high permeability and appealing selectivity due to their inefficient packing derived from a combination of ladder-like rigid segments with sites of contortion. However, it is recognized this class of polymers suffer from decrease in performance with time due to physical aging. The initial microporous structures approach a denser state via local chain rearrangements, leading to a dramatic reduction in permeability. As chain packing during film casting and physical aging are the key factors determine the performance in separation applications, characterization of the molecular mobility in these materials has been proved to provide valuable information. In recent research on PIM-1 the archetypal PIM, a molecular relaxation process with high activation energy together with a significant conductivity in the glassy state has been found and explained with the formation of local intermolecular agglomerates due to interaction of π-electrons in aromatic moieties of the polymer backbone. In this work, the dielectric behavior of the polymeric films and their response upon heating (aging) were measured by isothermal frequency scans during different heating/cooling cycles in a broad temperature range down to 133K for the first time. Multiple dielectric processes following Arrhenius behavior were observed. Local fluctuations, Maxwell-Wagner-Sillars (MWS) polarization and structural relaxations were discussed correlating to structural-properties of PIM-1. Up to now, no other work has studied the role of porosity and thermal history of PIM-1 film in dielectric processes. The goal is by eliminating thermal history and considering storing conditions provide better understanding on aging and plasticizing in high free volume glassy polymer PIM-1.
Offshore-Windenergieanlagen bilden einen zentralen Bestandteil der zukünftigen Energieerzeugung. Hierzu notwendige Gründungs- und Turmstrukturen werden vorrangig aus UP-geschweißten Blechen aus hochfesten niedriglegierten Stählen mit Dicken bis zu 200 mm hergestellt. Die großen Blechdicken begünstigen hohe Schweißeigenspannungen und lange Diffusionswege für z. B. über den Schweißprozess eingebrachten Wasserstoff. Damit steigt das Risiko für eine wasserstoffunterstützte Kaltrissbildung (WKB) an. Zum sichereren Ausschluss von WKB in den geschweißten Komponenten wird in Abhängigkeit der Nahtgröße, Wärmeeinbringung und Stahlsorte eine Mindestwartezeit (MWZ) von bis zu 48 h empfohlen, bevor die zerstörungsfreie Prüfung durchgeführt wird. Es ist allerdings offen, ob die empfohlene MWZ zu konservativ ist. Einflüsse sind hier bspw. die schwierige Bewertung des Wasserstoffdiffusionsverhaltens im heterogenen UP-Mehrlagen-Schweißgut (SG) im Vergleich zum Grundwerkstoff (GW).
Zudem sind nur sehr begrenzt H-Diffusionskoeffizienten für UP-Mehrlagen-SG als Grundlage zur Abschätzung des Zeitintervalls einer möglichen verzögerten Kaltrissbildung (somit MWZ) oder auch für Nachwärmprozeduren zur Wasserstoffreduktion (keine MWZ) verfügbar. Verlässliche H-Diffusionskoeffizienten sind daher ein adäquates Tool zur Bewertung des Risikos einer verzögerten WKB. Dieser Beitrag beschreibt Untersuchungen zur Charakterisierung der Wasserstoffdiffusionsverhalten in UP-Mehrlagen-SG eines 60 mm dicken Bleches einer Offshore-Stahlgüte.
Dazu wurden Proben unterschiedlicher Dicke aus dem reinen Schweißgut extrahiert und über elektrochemische Permeation und Trägergasheißextraktion im Temperaturbereich bis 400 °C sehr interessante Ergebnisse zu den korrespondierenden Diffusionskoeffizienten erarbeitet.
Pollution through emission of toxic gases is an increasing problem for the environment. It affects similarly agricultural, industrial and urban areas. In future, environmental emissions in ambient air must be monitored at even lower concentrations as nowadays. One environmental relevant compound is ammonia and its conversion product ammonium that have strong negative impact on human health and ecosystems. Most ammonia measurements in ambient air are performed in the range below 1000 nmol·mol 1 and thus there is a need for reliable traceable ammonia gas standards and in addition in situ analytical procedures for monitoring (in ambient air to avoid that thresholds are exceeded). Therefore, the use of reference materials is necessary for development accompanying test or for calibration, e. g. of structure-integrated sensors and mobile multi-gas sensors.
The developed gas standard generator produces gas mixtures that comply with the metrological traceability for ammonia gas standards in the desired environmentally relevant measurement range. The method is based on the permeation of ammonia through a membrane at constant temperature and pressure. The resulting ammonia penetrant gas flow is then mixed with a carrier gas flow to generate a gas standard flow of known concentration. The dynamic rage is enlarged by using a two dilution steps. Depending on the permeation rate, generable molar fractions are possible in the range nmol·mol-1 to a few µmol·mol-1. We present the design of an ammonia gas standard generator and first results of the characterisation of its individual components supporting the uncertainty assessment according to GUM for stable gas concentrations in this range. The relative uncertainty of the generated ammonia gas standard is smaller than 4 % (k = 2).
Pollution through emission of toxic gases becomes an increasing problem for the environment in agricultural, industrial and urban areas. In future, environmental emissions as well as ambient air must be monitored at even lower concentrations as nowadays. Consequently, demands arouse for measuring concentrations as low as the lower ppm or even ppb range. Current state-of-the-art technologies, as for instance electrochemical sensors, have reached their limits in this regard.
The developed ammonia gas standard generator produces standard gas mixtures which comply with the metrological traceability for ammonia gas standards in the desired environmentally relevant measurement range of e. g. 0.5 to 500 nmol/mol. This gas standard preparation method is based on the permeation of ammonia through a membrane at a constant temperature as well as the mixing of this permeated gas with a carrier gas to adjust a gas standard of known concentration. The ammonia gas standard is suitable for the calibration of standard optical methods, e. g cavity ring-down spectroscopy (CRDS) and multi-gas sensors.
The detection of gaseous ammonia in the lower ppm or even ppb range is obtained by incorporation of a fluorescent dye, which shows fluorescence enhancement in the presence of the analyte, into a polymer support being responsible for the accumulation of the analyte. The use of optical fluorescence as transduction mechanism enables high sensitivity as well as high temporal resolution. Here, we present first results on such a sensor system including the use of the developed gas standard generator for calibration issues. Additional benefits, particularly of fluorescence-based sensors, are their capability for miniaturization and potential multiplex mode. Beside the development of a highly sensitive and selective sensor, the integration of such systems into mobile sensor devices is addressed.
These sensors and sensor systems are developed and will be validated and operated in form of functional models for the application areas, structure-integrated sensors and mobile multi-gas sensors.
In the field of modelling hydrogen assisted cracking (HAC) phenomenon, hydrogen diffusivity is an important input parameter for numerical simulation. In terms of hydrogen diffusion coefficients, they have great impact on realistic assessment of the evolution of possible crack critical hydrogen concentrations. In addition, the chemical compositions of steels can have a strong effect on hydrogen diffusion. Unfortunately, literature provides a wide range of available hydrogen diffusion coefficients even for similar microstructures and equal temperatures. The scattering of the data can lead to significant deviations in the results of simulating the evolving hydrogen concentrations due to hydrogen uptake (by fabrication or service). Thus, the application of such data to crack-models or for component life tie predictions can be realized up to the present only by considering envelope curves of such value, corresponding to a work or bench case scenario, respectively. For improved reliability of numerical simulaitons, it is necessary to minimize the mentioned deviation of these data. Hence, this work focuses on the validation of hydrogen diffusion coefficients obtained from permeation experiments at room temperature. Two baintic steels with different alloying concepts were investigated, the creep-resistant 7CrMoVTiB10-10 and the reactor pressure vessel grade 20MnMoNi4-5. A numerical model is presented for simulation of the corresponding hydrogen diffusion during permeation experiments using the finite element software ANSYS. Three different diffusion coefficients (obtained from different common calculation methods) are considered and compared to numerical results. The vases of thes calculation methods are permeation transients which are a direct measure for hydrogen. The results of the simulated hydrogen diffusion coefficients show that only one procedure for calculation of diffusion coefficitnes is suitable in comparision to the experimental values. Thus, it is suggested to use this method for analysis of experimental results in case of hydrogen diffusion during permeation experiments. Furthermore, this work supplies validated values for the hydrogen diffusion coefficients of both steel grades.
In times of the energy revolution, the need for energy efficient separation processes promotes the advancement of new high performance materials for use as highly selective separation membranes. Most promising materials in this field, especially for gas separation, are polymers with intrinsic microporosity (PIMs) which were firstly introduced by Budd and McKeown. In this study the permeability of PIM-1 was increased by 439 % by formation of nanocomposites with only 1 wt% of polyhedral oligomeric phenethyl-silsesquioxane (PhE-POSS) within the polymer matrix. As the CO2/CH4 selectivity is fully retained, this leads to a shift in the Robeson plot towards the upper bound. The Robeson plot describes the current state of the art trade-off relation between selectivity and permeability of all known membrane polymers. As molecular mobility is a key factor for gas transport as well as the often observed physical aging of such polymers, our study also includes for the first time, molecular dynamics and conductivity of pure PIM-1 and PIM-1 nanocomposites as investigated by broadband dielectric spectroscopy (BDS).
Zur Basisabdichtung von Mülldeponien werden zunehmend polymere Abdichtungen mit Foliendecken zwischen 1 und 3 mm eingesetzt, die vielfach als absolut dicht gegenüber Sickerwässer und deren Inhaltsstoffen gelten. Durch Permeationsvorgänge ist jedoch mit Restdurchlässigkeiten zu rechnen, die auch bei technisch einwandfreien, intakten Folien auftreten. Es werden Meßmethoden vorgestellt, derartige Restdurchlässigkeitsraten an handelsüblichen Dichtungsbahnen für Deponiebasisabdichtungen zu messen. Als Permeenten dienen neben Sickerwasser aus einer Hausmülldeponie, konzentrierte, reine organische Lösungsmittel, deren Gemische untereinander und stark verdünnte Lösungen organischer Lösungsmittel in Wasser. Meßergebnisse werden angegeben und diskutiert.
Ammonia and its conversion product ammonium have a strong negative impact on human health and ecosystems. Most ammonia measurements in ambient air are performed in the molar fraction range (0.5 to 500) nmol/mol. There is a need for reliable traceable ammonia gas standards as well as in situ analytical procedures for the monitoring of ammonia in ambient air.
The permeation method is an effective tool for dynamically generating precise gas standards with a low uncertainty in the concentration range of a few nmol/mol to several µmol/mol in an inert carrier gas, e. g. pure nitrogen or purified ambient air. Here, we present our ammonia gas standard generator as well as results of the characterisation of its individual components supporting the uncertainty assessment according to GUM for stable gas concentrations in this range.
In order to detect ammonia in the nmol/mol-range, a suitable sensor has to be developed. In this contribution, we therefore additionally present first approaches on the development of such a sensor using optical fluorescence as transduction mechanism due to its intrinsically high sensitivity and high spatial resolution. Incorporation of a fluorescent dye, which shows fluorescence enhancement in the presence of ammonia, into a polymer matrix allows to reversibly recognize low amounts of ammonia. It can be concluded that fluorescence sensor is a robust tool for measurements of ammonia; however it needs calibration for the planed use.
Laboratory experiments on press hardened steels in different delivered states exposed to hydrogen
(2015)
The legal and economical demands in the automotive industry lead to increasing efforts reducing the CO2 emissions. A way to achieve that goal is to reduce the total weight of the car and therefore the fuel consumption. With the application of high strength steels in car body manufacturing it is possible to decrease the sheet thickness of the used materials and therefore the weight of the automobile. Components made of high strength steels can be produced by cold forming as well as by hot forming. In high strength steel the hydrogen content plays a crucial role for the component behavior. It is known that the hydrogen diffusivity and solubility are based on several factors, for example increasing dislocation density by cold working processes, vacancies, chemical composition and grain boundaries. The understanding and the control of the interaction between hydrogen and the high strength press hardened steels is an important factor for the application of the materials. The scope of this work is the determination of hydrogen diffusion and permeability kinetics in press hardened steel samples. An electrochemical hydrogen permeation method was applied on boron-manganese steel grades with different rolling reduction in initial ferrite/pearlite matrix as well as for the as-quenched martensite microstructure. The diffusible hydrogen contents of the specimens were measured using the carrier gas hot extraction technique (CGHE).
The key point within the scope of this research project was to find out whether there was a risk of creating an explosive atmosphere by permeation of flammable liquid compounds during transport of dangerous goods in freight containers under normal conditions of carriage. Therefore, all aspects that had an influence on the formation of such an atmosphere had to be considered. The most important influencing factors were permeation, air change in the freight container and ambient temperature. The first step was to investigate the permeation with different packaging materials, charge and temperatures. Furthermore, the air change rates of different freight containers were measured. A few climate tests with containers on ships, e.g. to Singapore, were performed to assess normal conditions of carriage. Another important point was measuring the solvent (toluene) concentration in the gas phase in a freight container loaded with plastic intermediate bulk containers (IBCs) filled with toluene. To confirm that the measured values were in the right range, the toluene concentration in the gas phase in a container was calculated with different packaging materials, air change rates and temperatures.
The results of the measurements and calculations have shown that safety layers in the packaging wall, e.g. the copolymer of ethylene and vinyl alcohol (EVOH) and polyamide, can reduce the rate of permeation by more than a decimal power, but the lower explosive limit of toluene is easily reached within a few hours at 40°C charge temperature if there is no barrier.
This document deals with the characterization of porous materials having pore widths in the macropore range of 50 nm to 500 µm. In recent years, the development of advanced adsorbents and catalysts (e.g., monoliths having hierarchical pore networks) has brought about a renewed interest in macropore structures. Mercury intrusionextrusion porosimetry is a well-established method, which is at present the most widely used for determining the macropore size distribution. However, because of the reservations raised by the use of mercury, it is now evident that the principles involved in the application of mercury porosimetry require reappraisal and that alternative methods are worth being listed and evaluated. The reliability of mercury porosimetry is discussed in the first part of the report along with the conditions required for its safe use. Other procedures for macropore size analysis, which are critically examined, include the intrusion of other non-wetting liquids and certain wetting liquids, capillary condensation, liquid permeation, imaging, and image analysis. The statistical reconstruction of porous materials and the use of macroporous reference materials (RMs) are also examined. Finally, the future of macropore analysis is discussed.
Ermittlung explosionsfähiger Gemische beim Gefahrguttransport unter normalen Beförderungsbedingungen
(2009)
Polyhedral oligomeric silsesquioxane with phenethyl substituents (PhenethylPOSS) as nanofiller was incorporated within Poly(bisphenol A carbonate) (PBAC) as matrix. Dielectric spectroscopy proved an almost complete miscibility of PhenethylPOSS up to 7 wt. %. At higher concentrations phase separation yields composites with a PBAC-rich matrix and POSS-rich domains which posses well shaped interfaces. The nanocomposites were also investigated with respect to their gas transport behaviour. An increase of the gas permeability was found at higher PhenethylPOSS concentrations, which is due to the phase separated structure.
Barrieren manchmal notwendig
(2008)
Barrier properties of plasma and chemically fluorinated polypropylene and polyethyleneterephthalate
(1995)
The functionalization, perfluorination or an coating of polypropylene (PP) and polyethyleneterephthalate (PET) surfaces in different plasma atmospheres and in an F[2] + N[2] gas mixture were investigated. The aim of this work was to form a barrier layer against solvent and fuel permeation. Typical test solvents were n-pentane, toluene, tetrachloroethylene and mixtures of n-pentane and methanol. The permeation was gravimetrically measured. The permeation of the solvent mixtures was analyzed by mass spectrometry and Fourier transform IR spectroscopy. The permeation of the solvent mixtures through the plasma-modified polymer samples was associated with increased absorption of polar solvent components in the polymer film. The thickness of the plasma-fluorinated PP surface layer was 10-100 nm and that of chemically fluorinated PP about 5000 nm. Nearly the same barrier efficiency was measured for both plasma- and chemically fluorinated samples.