Ingenieurwissenschaften und zugeordnete Tätigkeiten
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- 2010 (11) (entfernen)
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- Englisch (11) (entfernen)
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- Electron backscatter diffraction (3)
- Zinc borate (2)
- Aryl phosphate (1)
- Bisphenol-A bis(diphenyl)phosphate (BDP) (1)
- Burst pressure (1)
- CFD simulation (1)
- Charring (1)
- Dangerous goods (1)
- Dynamical simulation (1)
- Dünnschichte (1)
The classification of solid oxidizers according to the GHS (Globally Harmonized System of Classifica-tion and Labelling of Chemicals) and according to regulations on the transport of dangerous goods (based on the UN Recommendations/Model Regulations and implemented in all carrier domains as transport by road, railway, sea, air) is performed on the basis of the results of the UN test O.1 (―Test for oxidizing solids‖ described in chapter 34.4.1 in the Recommendations on the Transport of Danger-ous Goods, Manual of Tests and Criteria, Fifth revised edition, United Nations, New York and Geneva, 2009). This test was introduced into the UN Test Manual in 1995 as a replacement for a similar test from 1986. Even though the O.1 test is much better than the previous one there are still many prob-lems with this test. For this reason the IGUS-EOS working group (international group of experts on the explosion risks of unstable substances – working group: energetic and oxidizing substances) installed an ad-hoc working group in 2002 assigned with the task of proposing solutions for the existing prob-lems. The adequacy of such proposals has to be proven preferably by interlaboratory comparison (interlaboratory test) before they are presented to the UN Sub Committee for adoption into the UN Test Manual. The present report is the evaluation of an interlaboratory test which was designed by the Ad-hoc working group in order to find out whether the current method of comparing combustion times of test mixtures with those of reference mixtures is suitable in principle and whether some approaches for improvement of the method can be identified.
For the characterization of disperse and porous solids, usually single gas adsorption(GA) is employed. In the case of liquid adsorption (LA), the extraction of information on solids immediately becomes a more sophisticated matter since information on geometric as well energetic parameters of the solids is both superposed by liquid-mixture effects and displayed in excess terms. We have to ask if reliable solid parameters can be also obtained from LA isotherms. The enlarged data bank of gas and liquid adsorption measurements enables us to change systematically solid parameters (e.g., the pore width of MCM-41, the pore entrances of SBA-16, chemical heterogeneity) and to study in this way the influence of solid parameters on LA.
Structural changes in the condensed phase of bisphenol A polycarbonate (containing 0.45 wt% poly (tetrafluoroethylene))/silicone acrylate rubber/bisphenol A bis(diphenyl-phosphate) (PC/SiR/BDP) and PC/SiR/BDP/zinc borate (PC/SiR/BDP/ZnB) during thermal treatment in nitrogen atmosphere and in fire residues were investigated by solid-state NMR. H-1, B-11, C-13 and P-31 NMR experiments using direct excitation with a single pulse and H-1-P-31 cross-polarization (CP) were carried out including 31P(1 H) and C-13{P-31}double-resonance techniques (REDOR: Rotational Echo Double Resonance) on a series of heat-treated samples (580 K-850 K). Because many amorphous phases occur in the solid residues, and solid-state NMR spectroscopy addresses the most important sites carbon, phosphorus and boron, this paper is the key analytical approach for understanding the pyrolysis and flame retarding phenomenon in the condensed phase of PC/SiR/BDP and PC/SiR/BDP/ZnB.
For the system PC/SiR/BDP it is shown that (i) at temperatures around 750-770 K (main decomposition step) carbonaceous charring of PC occurs and arylphosphate structures are still present, reacted in part with the decomposing PC; (ii) for higher temperatures from 770 K the phosphorus remaining in the solid phase increasingly converts to amorphous phosphonates and inorganic orthophosphates with a minor amount of crystalline orthophosphates; and (iii) H-1-P-31{H-1} CP REDOR and H-1-C-13{P-31} CP REDOR NMR experiments suggest that the phosphates and phosphonates are bound via oxygen to aromatic carbons, indicating the interaction with the carbonaceous char.
When ZnB is added to the system PC/SiR/BDP, (i) ZnB leads to a slightly enhanced PC decomposition for temperatures below 750 K; (ii) alpha-Zn-3(PO4)(2) and borophosphate (BPO4) are formed in small amounts at high temperatures suggesting a reaction between BDP and ZnB during thermal decomposition; and (iii) most of the borate remains in the solid residues, forming an amorphous pure borate network, with the BO3/BO4 ratio increasing with higher temperatures.
The NMR data of thermal and fire residues are highly correlated, underlining the importance of this work for understanding the pyrolysis and flame retardancy mechanisms in the condensed phase during the burning of the PC/SiR blends. (C) 2010 Elsevier Ltd. All rights reserved.
Slip-rolling resistance of novel Zr(C,N) thin film coatings under high Hertzian contact pressures
(2010)
The present work was carried out within the framework of my four years activities as a scientific co-worker in the Working Group Tribological Optimization; Failure Analysis; Extreme Exposure in the division Tribology and Wear protection (VI.2) of the BAM Federal Institute for Materials Research and testing in Berlin, Germany and generously funded by the German Research Foundation (DFG WO521/6-1). First of all, I would like to express my sincere thanks to my supervisor Dr.-Ing. Mathias Woydt, head of the aforementioned working group, who gave me the opportunity to start my professional development, initiated and intensively supported this PhD work as well as accepted to take part in thesis committee. Prof. Dr. rer. nat. Walter Reimers, Chairman of the Institute for Materials Science and Technology of the Technical University of Berlin (TU Berlin), is also gratefully thanked for his interest in the thesis subject, for helpful comments and suggestions as well as for agreeing to participate in the referee of this work. I would like to thank also Prof. Dr.-Ing. Claudia Fleck, Chairman of the Material Engineering Department (Fachgebiet Werkstofftechnik) of the Technical University Berlin (TU Berlin), for assuming the chairmanship of the thesis committee. All the staff of the tribology division is also greatly acknowledged for bringing a pleasant working environment. Dr. Dirk Spaltmann is particularly thanked for the helpful discussions as well as for his assistance in English formulation. Dipl.-Ing. Manuel Reichelt and my bureau colleague Dr.-Ing. Géraldine Theiler will find here my many thanks for promoting constantly a good working atmosphere. Sigrid Binkowski and Dipl.-Ing. Norbert Kelling are also gratefully acknowledged for their constant and helpful technical support. André Otto is also thanked for his substantial administrative support. My sincere thanks go to Dr. rer. nat. (and “by the way” world and olympic champion in eights rowing) Ilona Dörfel (BAM V.1, Composition and Microstructure of Engineering Materials) for performing the highly relevant TEM investigations as also Heidemarie Rooch, and Ing. Wolfgang Gesatzke for the specific preparation of the samples. Furthermore, I greatly appreciate the contributions of Dr.-Ing. Vasile-Dan Hodoroaba, Birgid Strauß, Sigrid Benemann and Dipl.-Phys. Thomas Wirth (BAM VI.4) for their valuable contributions in microscopy analysis and to Dr.-Ing. Eric Wild (TU Berlin) for the substantial residual stress analysis of the coatings. Acknowledgement is also due to Dr. Thomas Chudoba from ASMEC GmbH for performing hardness measurements with his QCSM module. Thanks are surely extended to Fundación Tekniker, specifically Josu Goikoetxea and Dr. Javier Barriga for the manufacturing of the coatings in industrial deposition chambers and to the machining shop BAM Z.5 for the specimens preparation. Last, but by no means the least, I would like to thank all my friends for their support and to all the people who helped me directly or indirectly in my doctoral work and/or for my pleasant German adaptation. My very special thanks (du fond du coeur) go to my beloved parents Marie-Hélène (What is Tribology?) and Gérard (I miss you so much) and “of course” to my bright (and sometimes nerve-racking) sister Sophie, for everlasting encouragement and plenty of good advices in a wide range of domains. Ania, especially for your contribution in the decision of pursuing my “German experiment”.
Experimental investigation and CFD simulation of organic peroxide pool fires (TBPB and TBPEH)
(2010)
Time averaged mass burning rate (m˙′′f ), flame length (H), temperature (T ), irradi- ance (E) and surface emissive power (SEP ) of TBPB (tert -butyl peroxybenzoate) and TBPEH (tert-butyl peroxy-2-ethylhexanoate) pool fires are measured for six pool di- ameters (d = 0.059 m, 0.107 m, 0.18 m, 0.5 m, 1 m and 3.4 m) at BAM in house and outside test facility. The measured heats of combustion (–Δhc) of TBPB and TBPEH are 30113 kJ/kg and 34455 kJ/kg and the specific heat capacities at constant pressure (cp) are 1.8 kJ/(kg K) and 2.1 kJ/(kg K) respectively. The measured m˙′′f of TBPB and TBPEH pool fires are in the range of 0.37 kg/(m2 s)≤ m˙ ′′ f ≤ 0.83 kg/(m2 s) and show little dependence on the pool diameter d, and are four to sixty times higher (for d = 1 m) than that of hydrocarbon pool fires. It is shown that the mass burning rates of the investigated organic peroxides can be represented as an exponential function of the self-accelerating decomposition temperature (SADT). Low SADT implies that the organic peroxide pool fires burn at a much higher m˙′′f than hydrocarbon pool fires. Fuel Froude numbers (Frf) of TBPB and TBPEH are 5 to 100 times (depending on d) higher than for hydrocarbon pool fires. Due to higher Frf the H of TBPB and TBPEH (measured with a S-VHS Videocamera) are found to be two times larger (d = 1 m) than corresponding pool fires of hydrocarbons. Heskestads flame length correlation predicts the Hd (d = 3.4 m) of TBPB and TBPEH pool fires much better than Thomas and Fay correlations. The measured time averaged flame temperatures T (d = 3.4 m) for TBPB and TBPEH pool fires are in the range of 1400 K ≤ T ≤ 1500 K and are 200 K to 300 K higher than for JP-4, kerosene and gasoline. The irradiances of the TBPB and TBPEH pool fires measured by radiometers are E (Δy/d = 0.3) = 45 kW/m2 and E = 98 kW/m2 which are two to ten times higher in comparison to the corresponding n-pentane, super gasoline and diesel pool fires. So the thermal safety distances for organic peroxide pool fires are larger by a factor four in comparison to the hydrocarbon pool fires. An infrared thermography system is used for the determination of SEP of TBPB and TBPEH pool fires. The values of surface emissive power for TBPB and TBPEH are SEP (d = 3.4 m) = 196 kW/m2 and SEP = 258 kW/m2 and thus the SEP are by a factor of approximately two higher than for hydrocarbon pool fires. A self-sustained pulsating Hd (’W’-Effect) is found in TBPB pool flames and is further analysed to explain the reason of occurance on the basis of chemical structure of the fuel and discontinuous heat flux back from flame to the liquid pool. CFD simulations of TBPB and TBPEH pool fires at d = 0.18 m, 0.5 m, 1 m, 3.4 m and 8 m are carried out using the Unsteady Reynolds Averaged Navier Stokes (URANS) equa- tions. The three-dimensional geometries have been discritized with unstructured hybrid grids, with the number of cells in the range of 1 million. Depending on the grid resolu- tion and the pool diameter time steps of 0.0001 s ≤ Δt ≤ 0.01 s for the CFD simulations are used. For solving the discritized equations a finite volume based implicit solver AN- SYS CFX has been used. For modelling the combustion, stoichiometric combustion for both peroxides are assumed. The temperature dependence of the reaction rate has been determined by the Arrhenius approach. For modelling the combustion eddy dissipation concept (EDC) model has been used. For turbulence buoyancy modified k- � and SAS (Scale Adaptive Simulation) turbulence models are used. For the thermal radiation and soot mass fraction discrete transfer radiation model and Magnusson soot model have been used. A new method is suggested for the prediction of mass burning rate (m˙′′f ) by CFD simula- tion. Both peroxide pool fires show approximately constant mass burning rate indepen- dent of d whereas m˙′′f of TBPEH are under predicted at the beginning but show relatively good agreement with measurements for large pool diameters (d = 1 m). In case of TBPB the CFD simulation over predicts the mass burning rate m˙′′f of small TBPB pool fires and shows a continuous decrease with d. CFD predicts the flame length H close to the measured data provided that the constants in Thomas equation are modified. The CFD predicted time averaged surface emission flame temperatures of TBPB and TBPEH pool fires (d = 3.4 m, 1437 K and 1542 K) are in good agreement with the measured time averaged flame temperatures. The CFD predicted SEP for TBPB and TBPEH pool fires (d = 3.4 m, 217 kW/m2 and 288 kW/m2) are also in agreement with the measured values. From the CFD predicted irradiance ECFD it is possible to determine the thermal safety distances from large pool fires of hydrocarbons and organic peroxides.
EBSD is nowadays a common technique for the characterization of crystalline microstructures in scanning electron microscopy. The diffraction patterns are often interpreted by superimposing individual Kikuchi bands which are geometrically described by band edges derived from Braggs law. For the typically very simple crystal structures of technically applied materials, such a simplification of the Kikuchi pattern interpretation works sufficiently well, especially for orientation determinations as a main application of EBSD. The more complex crystal structures, however, are a challenge for EBSD indexing routines which in such cases often fail unpredictably. The use of only the intensities of single reflectors for a description of the Kikuchi band intensity and as a cut-off criterion for a pre-selection of the strongest bands are not satisfactory. Often the result will match too many phases, or there are certain deviations in the intensity prediction which must be adapted manually. This is already problematic if one is absolutely sure that the patterns are originating from the expected phase and it becomes a very questionable procedure for an unknown phase.
Bisphenol A polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) with and without bisphenol A bis(diphenyl phosphate) (BDP) and 5 wt.% zinc borate (Znb) were investigated. The pyrolysis was studied by thermogravimetry (TG), TG-FTIR and NMR, the fire behaviour with a cone calorimeter applying different heat fluxes, LOI and UL 94. Fire residues were examined with NMR. BDP affects the decomposition of PC/ABS and acts as a flame retardant in the gas and condensed phases. The addition of Znb results in an additional hydrolysis of PC. The fire behaviour is similar to PC/ABS, aside from a slightly increased LOI and a reduced peak heat release rate, both caused by borates improving the barrier properties of the char. In PC/ABS + BDP + Znb, the addition of Znb yields a borate network and amorphous phosphates. Znb also reacts with BDP to form alpha-zinc phosphate and borophosphates that suppress the original flame retardancy mechanisms of BDP. The inorganic–organic residue formed provides more effective flame retardancy, in particular at low irradiation in the cone calorimeter, and a clear synergy in LOI, whereas for more developed fires BDP + Znb become less effective than BDP in PC/ABS with respect to the total heat evolved.
Biofilms living on gold (Au) grains play a key role in the biogeochemical cycle of Au by promoting the dispersion of Au via the formation of Au nanoparticles as well as the formation of secondary biomorphic Au. Gold grains from Queensland, Australia, are covered by a polymorphic, organic-inorganic layer that is up to 40 μm thick. It consists of a bacterial biofilm containing Au nanoparticles associated with extracellular polymeric substances as well as bacterioform Au. Focused ion beam (FIB) sectioning through the biofilm revealed that aggregates of nanoparticulate Au line open spaces beneath the active biofilm layer. These aggregates (bacterioform Au type 1) resulted from the reprecipitation of dissolved Au, and their internal growth structures provide direct evidence for coarsening of the Au grains. At the contact between the polymorphic layer and the primary Au, bacterioform Au type 2 is present. It consists of solid rounded forms into which crystal boundaries of underlying primary Au extend, and is the result of dealloying and Ag dissolution from the primary Au. This study demonstrates that (1) microbially driven dissolution, precipitation, and aggregation lead to the formation of bacterioform Au and contribute to the growth of Au grains under supergene conditions, and (2) the microbially driven mobilization of coarse Au into nanoparticles plays a key role in mediating the mobility of Au in surface environments, because the release of nanoparticulate Au upon biofilm disintegration greatly enhances environmental mobility compared to Au complexes only.
Phosphorus-based flame retardancy mechanisms - Old hat or a starting point for future development?
(2010)
Different kinds of additive and reactive flame retardants containing phosphorus are increasingly successful as halogen-free alternatives for various polymeric materials and applications. Phosphorus can act in the condensed phase by enhancing charring, yielding intumescence, or through inorganic glass formation; and in the gas phase through flame inhibition. Occurrence and efficiency depend, not only on the flame retardant itself, but also on its interaction with pyrolysing polymeric material and additives. Flame retardancy is sensitive to modification of the flame retardant, the use of synergists/adjuvants, and changes to the polymeric material. A detailed understanding facilitates the launch of tailored and targeted development.