Three-Dimensional Imaging of Magnetic Domains with Neutron Grating Interferometry

This paper gives a brief overview on3D imaging of magnetic domains with shearing grating neutron tomography. We investigated the three-dimensional distribution of magnetic domain walls in the bulk of a wedge-shaped FeSi single crystal. The width of the magnetic domains wasanalyzed at different locations within the crystal. Magnetic domains close to the tip of the wedge are much smaller than in the bulk. Furthermore, the three-dimensional shape of individual domains wasinvestigated. We discuss prospects and limitations of the applied measurement technique

In Situ Imaging at Large-Scale Facilities

The importance of water management to successful cell operation of polymer electrolyte fuel cells PEFCs has directed the focus of extensive research activity on liquid water transport and its effect on cell performance, reliability, and durability of cell components. Water produced from the electrochemical reaction together with water from the humidified inlet gases maintains the hydration level of the membrane which is crucial for high proton conductance. However, excess liquid water can cause flooding of gas diffusion layer GDL regions and flow field channels, entailing oxidant starvation and significant power losses. Well balanced water management is a major challenge to achieve the optimal efficiency and lifetime of these cells [1 7]. In addition to water management, the formation and transport of CO2 bubbles on the anode side in direct methanol fuel cells DMFCs has to be understood in order to prevent blockage of anode side gas channels [8, 9]. In recent years, phosphoric acid based high temperature polymer electrolyte fuel cells HT PEFCs have attracted much attention from the fuel cell community because of the high CO tolerance. Owing to the high operating temperature of 160 amp; 9702;C, no liquid water is present in the cells and there is no need to humidify the gases. In order to achieve optimum power densities, the distribution of the electrolyte in the electrodes and the membrane plays a crucial role [10, 11]. In the recent past, imagingmethods have contributed a great deal to the advances in these research fields. Neutron and synchrotron X ray imaging have become established as indispensable diagnostic tools for the optimization of fuel cell components, for example, flow field geometry, GDLs or electrode structures, as they are able to reveal water transport processes in operating cells, CO2 bubble formation in DMFCs, or the dynamics of the phosphoric acid distribution in HT PEFCs in a non destructive way. In the following, basic principles of these methods and a representative selection of practical applications in fuel cell research are presente

3D microstructure modeling of compressed fiber-based materials

A novel parametrized model that describes the 3D microstructure of compressed fiber-based materials is introduced. It allows to virtually generate the microstructure of realistically compressed gas-diffusion layers (GDL). Given the input of a 3D microstructure of some fiber-based material, the model compresses the system of fibers in a uniaxial direction for arbitrary compression rates. The basic idea is to translate the fibers in the direction of compression according to a vector field which depends on the rate of compression and on the locations of fibers within the material. In order to apply the model to experimental 3D image data of fiber-based materials given for several compression states, an optimal vector field is estimated by simulated annealing. The model is applied to 3D image data of non-woven GDL in PEMFC gained by synchrotron tomography for different compression rates. The compression model is validated by comparing structural characteristics computed for experimentally compressed and virtually compressed microstructures, where two kinds of compression – using a flat stamp and a stamp with a flow-field profile – are applied. For both stamps types, a good agreement is found. Furthermore, the compression model is combined with a stochastic 3D microstructure model for uncompressed fiber-based materials. This allows to efficiently generate compressed fiber-based microstructures in arbitrary volumes

Electrolyte distribution and discharge time a combined study of X ray tomography and electrical measurements of a commercially available lithium ion capacitor

A lithium ion capacitor LIC was studied during an extensive charge discharge procedure. Changes in the interior threedimensional structure were investigated by means of X ray tomography during electrical cycling of the LIC. With increasing number of cycles we found electrolyte accumulating at the bottom of the capacitor. A clear correlation between electrolyte distribution at the bottom and performance of the LIC was determine

Large Area High Resolution Neutron Imaging Detector for Fuel Cell Research

Neutron radiography is increasingly being considered a powerful diagnostic tool in fuel cell research. Analyzing the water distribution for entire cells requires large and flexible fields of view and high spatial resolution at the same time. The combination of these requirements is a great technical challenge for neutron detectors: While conventional detectors could provide large fields of view, the accuracy of water mapping has so far been limited by their low spatial resolution. On the other hand, the applicability of sophisticated high-resolution detectors in fuel cell research is limited by their small and invariable fields of view.We present a novel detector system designed to meet the specific demands of fuel cell research. High spatial resolution of at the best 25 mu m was achieved by an optimized gadox scintillator, while a large and flexible field of view, e.g. 61.4 mm x 61.4 mm at a scale factor of 1:1 is provided by a 4096 x 4097 pixel(2) CCD-camera.The set up ensures great adaptivity to fuel cells of various sizes along with the best possible spatial resolution. Studies on the water transport in a DMFC and PEMFC are presented to demonstrate the capacity of the detector system. (C) 2011 Elsevier B.V. All rights reserved

Fuel Cell Research with Neutron Imaging at Helmholtz Centre Berlin

AbstractThis paper demonstrates the capabilities of the new instrument CONRAD II at Helmholtz Centre Berlin for the investigation of fuel cells. The performance gain of CONRAD II with respect to its predecessor instrument, CONRAD I, is demonstrated and different examples for in-operando measurements of polymer electrolyte membrane fuel cells are given. Furthermore, an application example for the high resolution detection system recently developed by the group is demonstrated which includes a three-dimensional measurement of the water distribution in a small fuel cell with a width of about 14mm by means of neutron tomography