Umschlagbahnhöfe aus entscheidungsorientierter Sicht

Trotz intensiver Fördermaßnahmen für die Bahn durch den Bund und die EU verlagert sich das Transportaufkommen immer weiter in Richtung der Straße. Nachteile der Bahn bestehen etwa in einer geringeren Durchschnittsgeschwindigkeit und Zuverlässigkeit sowie einer geringen Flexibilität. Durch die effiziente Planung des Containerumschlags in Umschlagbahnhöfen können die Nachteile der Bahn jedoch abgemildert werden. Dieser Beitrag beschreibt neben dem grundlegenden Aufbau von Umschlagbahnhöfen die wichtigsten strategischen, taktischen und operativen Planungsprobleme zur Ermöglichung eines effizienten Containerumschlags.

Simulation of dendritic-eutectic growth with the phase-field method

Solidification is an important process in many alloy processing routes. The solidified microstructure of alloys is usually made up of dendrites, eutectics or a combination of both. The evolving morphologies are largely determined by the solidification process and thus many materials properties are dependent on the processing conditions. While the growth of either type of microstructure is well-investigated, there is little information on the coupled growth of both microstructures. This work aims to close this gap by formulating a phase-field model capable of reproducing dendritic, eutectic as well as dendritic-eutectic growth. Following this, two-dimensional simulations are conducted which show all three types of microstructures depending on the composition and processing conditions. The effect of the dendritic-eutectic growth on the microstructural lengths, which determine materials properties, is investigated and the morphological hysteresis between eutectic growth and dendritic-eutectic growth is studied by employing solidification velocity jumps. Further, the influence of primary crystallization is investigated in large-scale two-dimensional simulations. Finally, qualitative three-dimensional simulations are conducted to test for morphological changes in the eutectic.Comment: 51 pages, 19 figure

Modellierung mehrkomponentiger Materialsysteme für die Phasenfeldmethode und Analyse der simulierten Mikrostrukturen

Der Erstarrungsprozess mehrkomponentiger Materialsysteme ist sowohl von großer wissenschaftlicher als auch von industrieller Bedeutung. Insbesondere die gerichtete Erstarrung mehrkomponentiger Hochtemperaturwerkstoffe ist für industrielle Anwendungen in Motoren oder Turbinen von besonderem Interesse. Im Rahmen dieser Arbeit wird der Erstarrungsprozess verschiedener mehrkomponentiger Hochtemperaturwerkstoffe mit der Phasenfeldmethode untersucht. Hierfür wird zunächst eine Methodik für die Verwendung thermodynamischer Datensätze in Phasenfeldsimulationen entwickelt und vorgestellt. Mit Hilfe dieser Methodik werden thermodynamisch konsistente Modelle der Hochtemperaturwerkstoffe NiAl-34Cr und Nb-Si generiert und mittels Phasenfeldsimulationen validiert. Anschließend werden für beide Systeme zwei- und dreidimensionale Phasenfeldsimulationen zur Untersuchung der zweiphasigen eutektischen Mikrostrukturentwicklung durchgeführt. Ziel dieser Studien ist die Identifikation von Schlüsselparametern für die Entwicklung der sich einstellenden Mikrostruktur während der gerichteten Erstarrung sowohl in geordneten eutektischen Strukturen als auch in Strukturen eutektischer Kolonien. Für die Untersuchung des Einflusses dieser Schlüsselparameter werden sowohl qualitative als auch quantitative Analysemethoden zur Untersuchung der Mikrostrukturen eingesetzt. Die vorliegende Arbeit umfasst eine vollständige Untersuchungskette von der Modellierung der Materialsysteme über die Durchführung repräsentativer Phasenfeldsimulationen bis hin zur Analyse der sich entwickelnden Mikrostrukturen

Modellierung mehrkomponentiger Materialsysteme für die Phasenfeldmethode und Analyse der simulierten Mikrostrukturen

Im Rahmen dieser Arbeit wird der Erstarrungsprozess der Hochtemperaturwerkstoffe mit der Phasenfeldmethode untersucht. Die vorliegende Arbeit umfasst eine vollständige Untersuchungskette, die sich von der Modellierung der Materialsysteme, über die Durchführung repräsentativer Phasenfeldsimulationen, bis hin zur Analyse der sich entwickelnden Mikrostrukturen erstreckt

High performance proton conducting membranes for fuel cells made by photopolymerization of hydrolytically stable monomers

Proton conducting membranes were prepared by photopolymerization of 2- acrylamido-2-methylpropane sulfonic acid solutions within the pores of polypropylene membranes. Several commercial and novel multifunctional monomers synthesized in IAS lab were investigated as suitable crosslinking agents for this application. Some membranes made with synthesized crosslinkers at low crosslinker concentrations exceeded 2.5 times the conductivity of Nafion® 115 membrane, while exhibiting a good hydrolytical stability, in contrast to the commercial crosslinkers based on multifunctional (meth)acrylates

Novel crosslinkers for high performance poly-AMPS-based proton exchange membranes for fuel cells

Polymer electrolyte fuel cells (PEFC) gained a lot of interest in recent years as a potential solution for an eco-friendly energy. Proton exchange membranes (PEM) are one of the main components of PEFCs and require mechanical and chemical stability to ensure high proton conductivity and effective separation of anode and cathode under challenging conditions. Best commercial membranes made from sulfonated fluoropolymers, such as Nafion®, are rather expensive. To improve fuel cell performance at a lower cost, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was investigated recently. 1 Since polyAMPS (PAMPS) excessively swells or even dissolves in water, we investigated several commercial crosslinkers and new multifunctional monomers (Fig. 1) to decrease swelling by crosslinking. AMPS, crosslinker and photoinitiator were dissolved in water and N-methyl-2-pyrrolidone (NMP), respectively. To facilitate conductivity measurements and handling of crosslinked PAMPS formulations after UVinitiated radical polymerization, they were constrained within a porous membrane using a procedure described by Zhou et al. 2 We tested several commercial crosslinkers and according to these results we developed new crosslinkers with enhanced hydrolytical stability and conductivity. In contrast to the commercial crosslinkers, where conductivity increased with increasing amount of crosslinker, our new acrylamide based crosslinkers needed only very low concentrations. They could achieve more than 2.5 times the conductivity of Nafion with only 5 wt% crosslinker. We used this novel crosslinkers to integrate them into asymmetric membranes with interpenetrating proton-conducting morphology for enhanced methanol barrier properties. 3 First results of their performance compared to Nafion will be presented. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. The authors would like to thank 3M for PP membrane samples and Ciba SC, Huntsman, Ivoclar Vivadent and Sartomer for samples of photoinitiator and crosslinker. 1 a) Qiao, J., et al., Journal of Materials Chemistry 2005, 15 (41), 4414-4423. b)Diao, H., et al., Macromolecules 43 (15), 6398-6405. 3 Zhou, J., et al., Journal of Membrane Science 2005, 254 (1-2), 89-99. 4 Radovanovic, P., et al., Journal of Membrane Science 2012, 401-402, 254-261

Novel crosslinkers for high performance poly-AMPS-based proton exchange membranes for fuel cells

Polymer electrolyte fuel cells (PEFC) gained a lot of interest in recent years as a potential solution for an eco-friendly energy. Proton exchange membranes (PEM) are one of the main components of PEFCs and require mechanical and chemical stability to ensure high proton conductivity and effective separation of anode and cathode under challenging conditions. Best commercial membranes made from sulfonated fluoropolymers, such as Nafion®, are rather expensive. To improve fuel cell performance at a lower cost, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was investigated recently. 1 Since polyAMPS (PAMPS) excessively swells or even dissolves in water, we investigated several commercial crosslinkers and new multifunctional monomers (Fig. 1) to decrease swelling by crosslinking. AMPS, crosslinker and photoinitiator were dissolved in water and N-methyl-2-pyrrolidone (NMP), respectively. To facilitate conductivity measurements and handling of crosslinked PAMPS formulations after UVinitiated radical polymerization, they were constrained within a porous membrane using a procedure described by Zhou et al. 2 We tested several commercial crosslinkers and according to these results we developed new crosslinkers with enhanced hydrolytical stability and conductivity. In contrast to the commercial crosslinkers, where conductivity increased with increasing amount of crosslinker, our new acrylamide based crosslinkers needed only very low concentrations. They could achieve more than 2.5 times the conductivity of Nafion with only 5 wt% crosslinker. We used this novel crosslinkers to integrate them into asymmetric membranes with interpenetrating proton-conducting morphology for enhanced methanol barrier properties. 3 First results of their performance compared to Nafion will be presented. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. The authors would like to thank 3M for PP membrane samples and Ciba SC, Huntsman, Ivoclar Vivadent and Sartomer for samples of photoinitiator and crosslinker. 1 a) Qiao, J., et al., Journal of Materials Chemistry 2005, 15 (41), 4414-4423. b)Diao, H., et al., Macromolecules 43 (15), 6398-6405. 3 Zhou, J., et al., Journal of Membrane Science 2005, 254 (1-2), 89-99. 4 Radovanovic, P., et al., Journal of Membrane Science 2012, 401-402, 254-261

Asymmetric sol-gel proton-conducting membrane

Proton-conducting membranes with interpenetrating polymer network morphology have gained attention in recent years for potential replacement of standard Nafion membranes in direct methanol fuel cells. These membranes generally consist of fine interpenetrating domains of proton-conducting and mechanically-supporting polymer phases, which often leads to improvements in mechanical strength and methanol barrier properties. Asymmetric sol-gel membranes comprising proton-conducting channels of cross-linked sulfonic acid functionalized ionomers embedded within a matrix of thermally-resistant, glassy polymer were prepared by photopolymerization starting from a polymer solution and evaluated in our laboratories. These membranes have an integral top skin layer with fine biomimetic proton-conducting channels, which provides a barrier against methanol crossover, on top of a coarser proton-conducting support. Conductivity of asymmetric membranes over a range of initial polymer concentrations and ion-exchange capacities (IEC) was just slightly lower than for the corresponding symmetric membranes. Methanol barrier properties of asymmetric sol-gel membranes were better than that of Nafion 115 membrane. The crosslinking agent functionality had a major effect on membrane conductivity. Use of trifunctional crosslinking agents resulted in significantly higher conductivities than those obtained with bifunctional agents, even surpassing the conductivity of Nafion membranes

Proton conducting membranes based on photopolymerizable monomers

The proton exchange barrier or Proton Exchange Membrane (PEM) is the critical part of a fuel cell. The basic function of the membrane is to enable proton transport, while being simultaneously impermeable for electrons and gas. Typically, membranes for the PEM fuel cells (PEMFC) are made of perfluorocarbon-sulfonic acid monomers. The best known material of this class is Nafion which has a unique interpenetrating structure of hydrophobic perfluorocarbon regions providing thermal and chemical resistance, mechanical strength and diffusional resistance combined with hydrophilic regions of water clusters surrounding charged sulfonic acid groups which allow selective proton transport. For these reasons, Nafion is still considered the benchmark against which most of the new materials are compared [1]. At the molecular level, proton transport may follow two principal mechanisms: (a) diffusion mechanism via H3O+ ion as a carrier and (b) proton hopping mechanism (Grotthuss transport) [2]. Contemporary PEMFCs are exclusively based on the vehicle mechanism. PEMFCs produce water as a by-product and H+ ions moving from the anode to the cathode pull water molecules by an electro-osmotic drag force. In addition, membrane suffers from evaporation of water at working temperatures of 60-90ºC. Nafion effectively conducts protons only when imbibed by water within a narrow range, which limits the operating temperature of PEM fuel cells to around 80oC. However an operating temperature above 100ºC is a highly desirable goal. PEM membranes are not dimensionally stable since the material significantly swells upon water absorption. Therefore the aim of our proton conducting membrane is a rigid polymer with perpendicular nano channels which are filled with a conducting sulfonic polymer where conductivity is mainly achieved by the Grotthuss mechanism. Several monomers and crosslinker in a broad range of concentrations in water and 1-Methyl-2-pyrrolidone (NMP) respectively were screened for their mechanical properties, water uptake and conductivity in porous membranes by photo polymerization with a polar photo initiator. As conductive polymer, primarily poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and poly(2-sulfoethyl methacrylate) (PSEM) respectively as well as polymers of phosphonic acid containing monomers or newly synthesized monomers were used. The conductive monomers were crosslinked with varying hydrophobic and hydrophilic multifunctional monomers like N,N'-methylene bisacrylamide (MBA), 2-Propenoic acid, 2-methyl-, 1,1'-(1,10-decanediyl) ester (D3MA) or polyethyleneglycol diacrylates with two varying chainlengths (PEG-DA700, PEG-DA330). The advantage of several different building blocks with known characteristics is the possibility to tune the polymer to special needs of an application. For example, some polymer compositions have good conductivity at lower temperatures whereas other polymers develop better properties at elevated temperatures. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat and with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. We thank 3M for providing us with samples of the PP membrane. 1/Hamrock, S.J. and M.A. Yandrasits, Proton Exchange Membranes for Fuel Cell Applications. 2006. 46(3): p. 219 - 244. 2/ Hoogers, G., Membranes and Ionomers, in Fuel Cell Technology Handbook G. Hoogers, Editor. 2002, CRC Press. p