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Eingeladener Vortrag
- nein (659)
Chemically unstable gases - flammability of ethylene oxide mixtures in sterilization processes
(2008)
Processed building rubble containing about 90 % of crushed concrete can be used as recycling aggregates. The reuse for the production of new high-grade concrete requires a knowledge of the engineering properties as well as the pore structure of These materials. Two recycling aggregates and the concretes made with them were studied.
Quantitative und qualitative Analyse von nanoskaligen Aerosolemissionen aus Industrieprodukten
(2008)
Die Struktur eines Materials bestimmt wesentlich dessen Gebrauchsverhalten. Diese einfache Weisheit ist Motivation für die ständige Weiterentwicklung des Untersuchungsinstrumentariums zur Gefügekennzeichnung von Baustoffen. Nachdem die Gefügeaufklärung insbesondere bei mineralischen Baustoffen bereits integrierter Bestandteil der Baustoffcharakterisierung ist, erhöht insbesondere die zunehmende Spezialisierung und Weiterentwicklung der Asphaltbaustoffe zusammen mit der Forderung nach gebrauchsgerechtem Leistungsnachweis den Bedarf an methodischer Entwicklung bei der Strukturkennzeichnung. Besondere Möglichkeiten zur tiefenaufgelösten und zerstörungsfreien räumlichen Visualisierung des Gefüges, der Ableitung strukturbeschreibender Kennwerte aber auch für eine anschließende Diskretisierung der inneren Struktur mittels finiter Elemente bietet das Verfahren der Computertomographie mit Röntgenstrahlen. Mit Hilfe verschiedener Anwendungen soll auf die Möglichkeiten dieser Methodik aufmerksam gemacht werden.
In order to clarify under which practical conditions real risks for hydrogen-induced stress corrosion cracking of prestressing steels exist laboratory investigations in aqueous solutions and concrete as well as tests with stressed prestressing steels were carried out. While different distances between steel and zinc (cathode and anode) showed only a negligible influence on the polarisation of the steel a significant dependence on the area ratio steel/zinc was observed. A critical area ratio of 10:1 can be defined above which polarisation of the steel to hydrogen evolution potentials is unlikely. The results obtained in the laboratory concerning the critical area ratio were confirmed by on-site investigations in a precasting plant. Exposure tests with hydrogen loading did not lead to fractures during the testing time for approved prestressing steels. The characteristic mechanical values determined immediately after the hydrogen loading tests did not show significant changes. Thus, an indirect contact between prestressing steels and galvanised elements can be estimated as uncritical. But a direct contact has to be excluded by compliance with DIN 1045-1, i.e minimal distance of 2 cm between prestressing steel and galvanised elements.
Chemiluminescence (CL) is a sensitive method of investigating the thermo-oxidative stability of polymers in the early stages of degradation. Therefore, CL measurements were applied to different automotive coatings to evaluate their degradation behavior during artificial weathering. In this work, CL measurements were carried out for different automotive coatings to follow their degradation behavior during artificial weathering. The CL emission depends on sample-specific parameters like stabilizer, matrix, or hardener; experimental parameters like the oxygen partial pressure; and exposure parameters like the duration of weathering. The potential of CL could be demonstrated by classifying materials into categories of good, medium, and low degradation performance at a much earlier stage of weathering exposure than in combination with the usual visual detection of weathering effects.
Thermally stimulated luminescence (TL) can be used to detect damage in the early stages of degradation after artificial weathering, and to analyze the efficiency of stabilizers used in automotive coatings. TL is particularly suitable for this task due to its inherent high sensitivity to structural, morphological, and chemical changes in macromolecular chains. In this work, TL measurements were carried out for different automotive coatings to follow their degradation progression during artificial weathering. The TL results demonstrate high sensitivity to parameters like stabilizers, matrices, hardeners, and weathering time, and provide an opportunity to monitor the early stages of damage in polymers, which therefore reduce the time required for further outdoor weathering tests.
Die Wirksamkeit einer Abtrennung aus Holz mit mindestens 50 mm Wandstärke für Zündmittel der Klassifizierung 1.4B konnte überzeugend bestätigt werden. Außerhalb dieser Abtrennung war überhaupt keine Wirkung zu beobachten. Auch wenn die Originalverpackung leichterer Bauart vergleichsweise stark beschädigt wurde fungierte die hölzerne Abtrennung aus wirksamer Schutz gegen die entstandenen Splitter. Einer weiteren Anwendung der bisherigen Verfahrensweise steht aus sicherheitstechnischer Sicht nichts im Wege.
Tribological screening tests (simple, reciprocating ball-on-flat tests) were performed with the objective to identify an appropriate coating for the articulating surfaces of artificial hip joints whose acetabular cups and femoral stems are made from Ti6Al4V alloy, which is appreciated for its light weight, good biocompatibility and elastic properties similar to those of natural bone. Standard coatings like TiN or CrN performed better than more complicated multi-layer systems, though not as good as different types of amorphous carbon coatings, generally referred to as diamond-like carbon or DLC coatings. Among the latter, hydrogenated amorphous carbon (a-C:H) displayed the best properties, especially if the hydrogen content was increased by reducing the bias voltage during PA-CVD-deposition.
The optimised a-C:H coating revealed the most promising wear behaviour under the applied testing conditions, i.e. the increase of linear wear with the number of cycles was close to zero. Regarding the materials examined in this study, correlation of wear with mechanical properties obtained by nano-indentation revealed that high hardness was not an adequate criterion for selecting appropriate coatings. A high ratio of hardness and elastic modulus (H/E) proved to be more important. Microstructural and micro-analytical investigations revealed transformation of TiN and CrN to TiO2 and Cr2O3, respectively, and amorphous carbon was, at least partly, transformed to graphite. Furthermore, incorporation of Al2O3 from the ball was observed at a very fine scale. The wear debris of favourable coatings always formed agglomerates of nano-scale particles. It was shown that commercial nano-particles of Al2O3, Cr2O3 and carbon black are comparable to particles generated by the tribological tests. However, it is uncertain whether they are comparable to those formed during simulator studies or in vivo. Furthermore, the performance of the favourable coating has to be tested in a hip joint simulator before its potential for application in prostheses can be assessed.
Geosynthetic clay liners (GCLs) often have a sandwich-like multilayer structure, e.g. bentonite encased between two geotextile layers connected by fibers or yarns, either by needle-punching or stitch-bonding. Therefore, the internal shear strength of the GCL depends on the strength of reinforcing fiber bundles or yarns and their anchoring strength in the cover and carrier geotextiles. When used on long and steep slopes and covered with thick soil layers, the GCL is permanently exposed to a combined action of compressive and shear stress. Such load conditions are characteristic for landfill covers and the slope stability of the overall cover system in the long run strongly depends on the long-term internal shear strength of the GCL. A new test method was developed to study this long-term shear behavior. The focus was not only on creep, as it is normally done, but on aging effects. The shear test devices allow the measurement of creep curves and times-to-failure at elevated temperatures in different media (tap water and de-ionized water). In this publication, the main findings of the experiments on needle-punched GCLs with and without thermal treatment are summarized. Tap water as a test medium was essential to ensure sodium to calcium ion exchange in the bentonite layer. Under this condition extremely long test durations without failure were achieved. Sliding failure occurred when de-ionized water was used. Two failure modes were observed: brittle failure of the GCLs with thermal treatment and slow disentanglement of fiber bundles for untreated GCLs. Short-term shear strength (e.g. peel strength) is unrelated to the actual long-term shear strength, i.e. to the times-to-failure achieved in long-term shear strength test. Hence, short-term shear strength alone will not provide reliable dimensioning data for product design and choice of resins. Therefore, the often suggested approach, namely, restriction to short-term tests only and application of factors of safety, is challenged by these results.
Highly soluble 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-(DOPO)-based diamino hardener (2), bearing its amino groups directly on the DOPO framework, is investigated with respect to its use as a reactive flame retardant in thermosets. A mechanism for decomposition of the corresponding phosphorus-modified epoxy resin system based on a diglycidylether of bisphenol A DGEBA and 2 (DGEBA/2) is proposed and compared to the systems using DGEBA and 4,4'-diaminodiphenylsulfon (DGEBA/DDS) and to a similar system based on the structurally comparable non-reactive DOPO-based compound (DGEBA/DDS/1). Additive 1 changed the decomposition characteristics of the epoxy resin only slightly and phosphorus was released. Incorporating 2 induces two-step decomposition and most of the phosphorus remains in the residue. Furthermore, the fire behaviour of neat epoxy resin systems and a representative carbon fibre-reinforced composite based on DGEBA, DDS and 2 (DGEBA/DDS/2) were examined and compared to that of the analogous composite systems based on DGEBA/DDS and DGEBA/DDS/1. Based on different flame retardancy mechanisms both the reactive compound 2 and the additive compound 1 improve flammability (increase in LOI >13% and achieving V-1 behaviour) of the epoxy resin and composites. Under forced flaming only the flame inhibition of the additive compound 1 acts sufficiently. Lastly, the superior key mechanical properties of the epoxy resin and composite based on 2 are sketched.
Praktische Beispiele und Erfahrungen zu Störfallauswirkungsbetrachtungen - Freistrahlberechnungen -
(2008)
Damit Edelstahl rostfrei bleibt - Korrosionsschutzgerechte Verarbeitung von Edelstahl Rostfrei
(2008)
Damit Edelstahl rostfrei bleibt - Korrosionsschutzgerechte Verarbeitung von Edelstahl Rostfrei
(2008)
Molecular dynamics of ultrathin supported polysulfone films studied by dielectric spectroscopy
(2008)
Charakterisierung typischer Defektstrukturen in modernen Werkstoffen mittels Computertomographie
(2008)
Crack growth tests have been performed at 950 °C with Single Edge Notch specimens of the Ni-based single crystal superalloy PWA1483. In particular, several orientations and frequencies have been investigated, thus allowing the assessment of the influence of these parameters on the crack growth rate. In addition, oxidation experiments have been carried out to characterize the kinetics of the outer oxide scale growth at the same temperature.
On the other side, crack growth has been simulated with the Finite Element program ABAQUS in real test conditions by the node release technique. The nodes are released according to the measured crack growth rate.
The simulation results are compared with the test results on the basis of the computed Crack Tip Opening Displacement (CTOD). For this purpose, the crack is propagated until a stabilized value of the CTOD is obtained. This is usually the case when the crack has crossed the initial plastic zone. The procedure provides an evaluation of the effects of cycle frequency, crystal orientation, plasticity and oxide induced crack closure.
After having checked in a previous study the influence of stroke and normal load in laboratory fretting tests accomplished with thin steel roping wires, in this paper the effect of the contact pressure (test configuration), environmental conditions (relative humidity) and reduction of the friction coefficient (lubricants) on the wear behaviour were analysed. The wires were 0.45 mm in diameter and the material was a cold-drawn eutectoid carbon steel (0.8% C) with a Tensile Strength over 2800 MPa. The tests were performed on an oscillating test rig and the volumetric wear of both specimens of the tribocouple was determined separately from three-dimensional topographies of the wear scars acquired by means of a confocal profiler, and a calculation algorithm developed in using MATLAB®. The strong effect of humidity and lubrication on wear behaviour was proved, whereas a slight effect of contact pressure was derived.
Laser-induzierte Zerstörung von optischen Komponenten bei Anwendung von Femtosekunden-Impulsen
(2008)
Über einen Zeitraum von drei Jahren wurde im Rahmen eines europäischen Forschungsprojekts das Verhalten von Feuerwerkskörpern unter unterschiedlichsten Bedingungen untersucht, um damit die Vorgänge bei der Explosion eines Feuerwerkslagers besser bewerten und einschätzen zu können. Schwere Unfälle in Lagern von Feuerwerk, wie z. B. im Jahre 2000 im niederländischen Enschede, ließen die Frage aufkommen, ob die mit verhältnismäßig kleinen Mengen ermittelten Gefahrgutklassifizierungen auch noch im Containermaßstab Gültigkeit besitzen und ob das Verhalten korrekt vorhergesagt wird. Diese Frage war nicht zuletzt nur durch Versuche im Vollmaßstab zu beantworten, die eine zentrale Rolle in diesem Projekt spielten. Darüber hinaus richtete sich ein Teil der Arbeit darauf, im Falle abweichender Ergebnisse zwischen regulären Gefahrgutprüfungen und realistischen Versuchen im Vollmaßstab die Zusammenhänge aufzudecken und eine andere oder modifizierte Prüfmethodik vorzuschlagen, die korrekte Aussagen für sehr große Mengen Feuerwerk liefert. Zu diesem Aspekt wurden interessante Ergebnisse mit einer Druckkammer gewonnen, wobei diese Arbeiten noch fortzusetzen sind.
Ideally, bioactive ceramics for use in alveolar ridge augmentation should possess the ability to activate bone formation and, thus, cause the differentiation of osteoprogenitor cells into osteoblasts at their surfaces. Therefore, in order to evaluate the osteogenic potential of novel bone substitute materials, it is important to examine their effect on osteoblastic differentiation. This study examines the effect of rapidly resorbable calcium-alkali-orthophosphates on osteoblastic phenotype expression and compares this behavior to that of β-tricalcium phosphate (TCP) and bioactive glass 45S5. Test materials were three materials (denominated GB14, GB9, GB9/25) with a crystalline phase Ca2KNa(PO4)2 and with a small amorphous portion containing either magnesium potassium phosphate (GB14) or silica phosphate (GB9 and GB9/25, which also contains Ca2P2O7); and a material with a novel crystalline phase Ca10[K/Na](PO4)7 (material denominated 352i). SaOS-2 human bone cells were grown on the substrata for 3, 7, 14, and 21 days, counted, and probed for an array of osteogenic markers. GB9 had the greatest stimulatory effect on osteoblastic proliferation and differentiation, suggesting that this material possesses the highest potency to enhance osteogenesis. GB14 and 352i supported osteoblast differentiation to the same or a higher degree than TCP, whereas, similar to bioactive glass 45S5, GB9/25 displayed a greater stimulatory effect on osteoblastic phenotype expression, indicating that GB9/25 is also an excellent material for promoting osteogenesis.
Nanoindentation and electron microscopy of bony tissue around biofunctionalized titanium implants
(2008)
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.
Für den Explosionsschutz in Biogasanlagen ist es erforderlich, die Explosionsgrenzen des Gases in Luft zu kennen. Biogase aus landwirtschaftlichen Anlagen haben jedoch eine schwankende Zusammensetzung, sodass für jede Gemischzusammensetzung die Explosionsgrenzen experimentell bestimmt werden müssten. Dies ist i. d. R. mit erheblichem Aufwand verbunden. In diesem Beitrag wird eine Methode vorgestellt, bei der mithilfe von zwei Explosionsdiagrammen die Explosionsgrenzen von Biogas mit bekannter Zusammensetzung abgeschätzt werden können. Dabei werden neben dem Methan- und Kohlendioxidanteil des Biogases auch mögliche Anteile von Wasserdampf berücksichtigt.
Validation process
(2008)
Langzeit-Monitoring an den Spannbetonbrücken des neuen Hauptbahnhofs Berlin (Lehrter Bahnhof)
(2008)
Spannbetonbrücken des neuen Hauptbahnhofs in Berlin, die etwa 170 m lang sind und auf 12 Stützen ruhen, werden für viele Jahre mit einem Monitorsystem überwacht. Gemessen werden langzeitig auftretende Setzungen und Hebungen an den Auflagerpunkten. Für die Messungen wird ein hydrostatisches und ein laseroptisches System für die vertikalen Verformungen eingesetzt, daneben Neigungsmesser und Dehnungsaufnehmer (elektrische und faseroptische) sowie Temperatur-Sensoren. Für die Auswertung wird eine neuartige Symbiose von experimenteller und mechanisch-numerischer Analyse angewendet.
Structure determination of two asymmetrically substituted oxadiazoles from powder diffraction data
(2008)
The crystal structures of the 1,3,4 oxadiazole compounds N,N-dimethyl-N-[4-(1,3,4-oxadiazol-2-yl)phenyl]amine (1) and 2-methyl-5-phenyl-1,3,4-oxadiazole (2) have been determined. In case of 1 no adequate crystals were available; therefore the structure was solved at room temperature from X-ray powder diffraction data using the method of simulated annealing. This solution is compared to a second one obtained by applying the molecular replacement method. Subsequent Rietveld refinements combined with the so called two stage method based on the data collected to 1.6 Å resolution yielded an Rwp value of 7.27% for 1. Compound 1 crystallizes in the orthorhombic space group P212121 with lattice parameters of a = 7.599(4) Å, b = 6.004(2) Å, c = 21.736(3) Å. The crystal structure of 2 was solved by means of single crystal structure analysis (monoclinic space group P21/c, a = 8.010(3) Å, b = 10.783(4) Å, c = 19.234(7) Å, β = 90.794(9)°).
Silicon substituted Hydroxyapatite coatings were prepared by Pulsed Laser Deposition
from targets made of mixtures of Hydroxyapatite with Si powder at different concentrations. The
properties of the Si-HA coatings with several degrees of Si substitution were analyzed by different
techniques such as FTIR, XRD, XPS and solid-state NMR. It was found that the Si incorporation
causes an amorphization of the structure together with a loss of carbonate groups. Furthermore, the
Si atoms are incorporated in the form of SiO4
4- groups, and H(PO4)2- appears as the predominant
phosphate group.
The results of a combined structural characterisation (XRD, IR, NMR, SEM, TEM) of a
phosphate containing Mg-Ca silicate and a phosphate containing Na-Ca silicate glass samples are
presented. The structural results are also compared with in vitro tests carried out in simulated body
fluids for checking bioactivity.
Most of the methane (CH4) emission from rice fields is derived from plant photosynthates,
which are converted to CH4. Rice cluster I (RC-1) archaea colonizing the
rhizosphere were found to be the methanogens responsible for this process. Hence, RC-1
methanogens seem to play a crucial role in emission of the greenhouse gas CH4. We
determined the community composition and activity of methanogens colonizing the
roots of eight different rice cultivars after growth on both Italian rice soil and river bank
soil, which contained different communities of methanogenic archaea. The community
composition was analyzed by terminal restriction fragment length polymorphism and
cloning/sequencing of the archaeal 16S rRNA gene and the mcrA gene coding for a
subunit of the methyl coenzyme M reductase. When grown on rice field soil, the
methanogenic community of the different rice cultivars was always dominated by RC-1
methanogens. In contrast, roots were colonized by Methanomicrobiales when grown on
river bank soil, in which RC-1 methanogens were initially not detectable. Roots
colonized with Methanomicrobiales compared with RC-1 exhibited lower CH4 production
and CH4 emission rates. The results show that the type of methanogens colonizing
rice roots has a potentially important impact on the global CH4 cycle.
GHS - Physical Hazards
(2008)
Our group previously synthesized 99mTc-labeled fatty acids suitable for myocardial metabolism and flow imaging. In this set of experiments, 29 new analogues were synthesized according to the 4 + 1 mixed ligand approach with some specific differences. Conventional 4 + 1 99mTc-fatty acids are built in the sequence: Tc-chelate, alkyl chain, and carboxylic group. We developed compounds following a new design with the sequence: carboxylic group, alkyl chain, Tc-chelate, and lipophilic tail. Therefore, the 99mTc-chelate was transferred to a more central position of the compound, aiming toward an improved myocardial profile and an accelerated liver clearance. In this context, several functional groups incorporated in the lipophilic tail section were tested to evaluate their influence on the compound's character. In addition to biodistribution studies in vivo, the myocardial first-pass extraction of the compounds was tested in an isolated Langendorff rat heart model. A satisfactory myocardial uptake of up to 20% of the injected dose (% ID) in the perfused heart and a fast liver clearance in vivo with only 0.29% ID/g at 60 min postinjection demonstrate that the induced molecular modifications affect the kinetics of 99mTc-radiolabeled fatty acid compounds favorably. From the data set, rules for estimating the biodistribution of fatty acids tracers are deduced.