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Abstract: We present two different methods to increase the size of available neutron beams in order to allow for the investigation of large objects. Application of these methods is demonstrated for radiographic imaging of fuel cells. The first approach is a scanning procedure based on the coordinated translation of detector and sample through the beam. Further advancement was achieved by installing a focusing neutron guide, which offers an expanded neutron beam size after diverging from a focused point source. [Copyright &y& Elsevier]

In this study, we report the first case of non-destructive characterization of the dependence of the flux trapping mechanism on the grain properties of a bulk type II superconductor using a combination of polarized neutron tomography and diffraction contrast tomography. The high temperature superconductor, YBa 2 Cu 3 O 7 −δ , has been used in this study due to its viable commercial growth processes typically resulting in the production of polycrystalline specimens. The diffraction tomography revealed the pseudo-single crystal nature of the sample i.e. a polycrystalline sample with 47 composite grains having a maximum grain misorientation angle of 1.86°. Polarized neutron tomography was used for characterization of the flux trapped in the material after field cooling to 90.5 K in a field of 0.5 mT and switching off the field. A combination of the results from these two non-destructive characterization techniques indicate a correlation between the anisotropy of the trapped flux with the orientation of the grains in the material in addition to a preference for the flux trapping in the grain boundaries. • Non-destructive field & grain characterization in YBCO via neutron tomography • Grain reconstruction reveals pseudo-single crystal nature of sample. • Trapped field direction correlate with grain orientation. • Field trapping correlate with grain boundaries. [ABSTRACT FROM AUTHOR]

Abstract: Rocks are commonly very heterogeneous materials. Randomly distributed micro-flaws inside the rock are believed to initiate tensile cracks from which shear fractures develop and coalescence through en echelon interactions leads to fracture. In this paper, we describe the results of applying high-resolution X-ray tomography to samples of greywacke and limestone experimentally deformed under unconfined axial shortening at various loads equivalent to different fractions of the sample strength. Mineral grains, pores, micro-cracks and other voids were imaged with a resolution of 10μm. 3D image analysis enabled us to monitor the initial state of the samples and the changes in them due to compression. Crack morphology is characterized and compared to the micro-structure of the sample before and after deformation. In the greywacke, formation of a macro-crack ∼10° oblique to the stress direction is observed. It initiated in fine intergranular material at the top tip of the sample and is composed of tensile fractures connected by wing cracks. None of the voids defined in the initial state fractured, and the crack is interpreted to have started either as a micro-crack which was smaller than the resolution of the tomography, or, as a completely new crack. In the limestone, cracks are observed to initiate in features that are too small to be imaged by the tomography, or also in newly created cracks. [Copyright &y& Elsevier]

Metal foam flow-fields have shown great potential in improving the uniformity of reactant distribution in polymer electrolyte fuel cells (PEFCs) by eliminating the 'land/channel' geometry of conventional designs. However, a detailed understanding of the water management in operational metal foam flow-field based PEFCs is limited. This study aims to provide the first clear evidence of how and where water is generated, accumulated and removed in the metal foam flow-field based PEFCs using in-operando neutron radiography, and correlate the water 'maps' with electrochemical performance and durability. Results show that the metal foam flow-field based PEFC has greater tolerance to dehydration at 1000 mA cm−2, exhibiting a ~50% increase in voltage, ~127% increase in total water mass and ~38% decrease in high frequency resistance (HFR) than serpentine flow-field design. Additionally, the metal foam flow-field promotes more uniform water distribution where the standard deviation of the liquid water thickness distribution across the entire cell active area is almost half that of the serpentine. These superior characteristics of metal foam flow-field result in greater than twice the maximum power density over serpentine flow-field. Results suggest that optimizing fuel cell operating condition and foam microstructure would partly mitigate flooding in the metal foam flow-field based PEFC. Image 1 • Neutron imaging applied to water management in metal foam flow-field based PEFC. • The metal foam flow-field enhances the uniformity of water distribution. • The metal foam flow-field improves the tolerance to dehydration. • The metal foam flow-field is susceptible to flooding at low current density. [ABSTRACT FROM AUTHOR]

Abstract This manuscript presents the effect of the solid phase corrugation of low density flexible cellular polymers on both their mechanical and thermal properties. First, a detailed quantification of solid phase corrugation has been carried out by means of high resolution synchrotron micro-tomography in a collection of polyethylene foams. Subsequently, the collapse stress in compression has been analysed both from the theoretical and experimental points of view achieving a clear relation between the solid phase corrugation and the ratio of theoretically calculated and experimentally measured collapse stress. Finally, solid phase corrugation has been correlated with the thermal expansion coefficient at room temperature. Graphical abstract Unlabelled Image Highlights • The corrugation of the solid phase of a collection low density cellular polymers was calculated by image analysis. • Two image analysis protocols were developed and applied in high resolution synchrotron X-ray tomographies. • The corrugation is the responsible of the decrease of experimental collapse stress from its ideal theoretical value. • The thermal expansion coefficient suddenly increase at 25 °C due to solid phase corrugation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A multi-scale tomographic approach was used to study the structure of polymeric foams. • Gaseous phase features were examined using conventional lab-scale X-ray tomography. • Solid phase parameters were analysed by means of synchrotron X-ray tomography. • A novel analysis method to separate the solid phase in struts and walls was developed. Abstract This manuscript presents a detailed characterization of the cellular structure of two types of polymeric foams by non-destructive multi-scale X-ray computed micro-tomography. This comparative study is conducted in two different polymeric materials –rigid polyurethane foams and cross-linked low density polyethylene foams-. Based on this technique and using 3D image analysis, conventional descriptors of the foams gaseous phase (cell size distribution, mean cell size and anisotropy ratio) are characterized at a standard voxel size of 5 µm. Complementarily, 0.4 µm voxel size synchrotron X-ray tomography data sets have been used to characterize, using a new image analysis approach, features of the solid phase of the foams (fraction of mass in the struts and thickness of the different entities of the solid architecture: struts and walls). The presented methodology, based on multi-scale tomographic analysis, allows obtaining a better understanding of the connection between foaming process and cellular structure and is important to gain knowledge on the structure-properties relationships for these materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design and Implementation of Polarized Neutron Imaging for the first time on IMAT imaging station at ISIS Neutron and Muon Source. • Validation of the system via characterization of the homogeneous magnetic field produced from a solenoid. • Magnetic characterization of additively manufactured MnAl samples indicate their magnetic anisotropy can be engineered via optimization of scan parameters. In this study, we report the first case of design and implementation of a polarized neutron imaging option on the Imaging and Materials Science & Engineering Station (IMAT). This is a significant addition to the capabilities of the station that allows the characterization of advanced magnetic materials for different engineering applications. Combining its time-of-flight feature with a polarized beam yields data that facilitate both quantitative and qualitative analysis of magnetic materials. Using the simple field of an aluminium solenoid, we perform a characterization of the new setup. In addition, we present polarized measurements of additively manufactured (AM) MnAl samples where the magnetic anisotropy due to the fabrication process has been investigated as a first scientific application of the setup. The results indicate that the anisotropy of the material can be engineered through variation of the AM fabrication parameters. [ABSTRACT FROM AUTHOR]

During solidification of Fe-containing Al-Si casting alloys, various different intermetallic phases are formed. As this can have an impact on mechanical properties we investigated phase formation by applying in-situ time resolved synchrotron X-ray tomography. For a commercially pure Al-10Si-0.3 wt.% Fe alloy, phase morphology and spatial arrangement during solidification was revealed with 1 °C temperature resolution. We find that many of the intermetallic phases that have been identified as β-AlFeSi phases in previous studies are in fact δ phases. It was found that δ plates mainly nucleate on the eutectic Al and Si. δ phase formation terminates almost simultaneously with the final solidification of eutectic phases. Features of δ phase growth such as impingement, branching and deformation of plates are discussed. The phase separation sequence during solidification is described and explained by the existence of “cells” of residual liquid in which δ phase formation progresses rapidly due to the supersaturation of solute atoms. [ABSTRACT FROM AUTHOR]

In this work, pore network modelling was used to investigate the role of the microporous layer (MPL) in the redistribution of phosphoric acid (PA) in a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) gas diffusion electrode (GDE). A HT-PEMFC GDE composed of a catalyst layer (sprayed in-house), MPL, and fibrous substrate was assembled, and its three-dimensional (3D) geometry was imaged using synchrotron X-ray microcomputed tomography. The spatial distribution of pore spaces and their connections were identified based on the 3D geometry, and an equivalent pore network of the GDE was obtained for simulating the PA transport with an invasion percolation algorithm. The predicted mass redistribution of PA in the GDE was found to be in excellent agreement with experimental values reported in the literature. The presence of the MPL was found to encourage the redistribution of PA within the CL and inhibited PA leaching toward the channel. To the authors’ best knowledge, this study is the first numerical simulation of PA transport in a HT-PEMFC GDE. [ABSTRACT FROM AUTHOR]

Abstract: Liquid metallic alloys with and without stabilizing particles such as TiB2 or SiC were processed to single films or artificial single Plateau borders to clarify the stabilization mechanisms of metallic foams based on the same melts. First, isolated single films were pulled out of a liquid metal by using circular wire frames of various sizes. Modified wire frame structures comprising double or quadruple parallel frames were then used to create artificial metallic Plateau borders. Drainage in single metallic films between two Plateau borders was studied by cutting films vertically and analysing their cross sections. Particle movement in liquid films was observed in-situ via synchrotron X-ray radioscopy. It was found that Mg-free liquid metallic alloys containing stabilising particles are less stable and rupture immediately because of unhindered drainage. In contrast, films made of AlSi9Mg0.6 alloy containing TiB2 or SiC are stable for long holding times. Our study shows that the complexity of drainage and evolution of Plateau borders in true metal foams can be studied by using a simple model system based on a single metallic film between two artificial Plateau borders. [Copyright &y& Elsevier]

Abstract: The influence of surface treatment and design of cathode flow fields in direct methanol fuel cells was investigated by in-plane neutron radiography and measurements of cell performance and pressure drop along the cathode channels. A specially designed test cell and neutron radiography set-up allows for studying the water distribution in an in-plane viewing direction. A temporal resolution of down to 10 s was used while an image resolution of approximately 80 μm could be obtained. The cathode flow fields were either impregnated by a hydrophobizing or hydrophilizing agent or left untreated. It turned out that hydrophobic channel walls lead to the formation of large water droplets, which partially block the air flow in the cathode channels. Their periodical growth and discontinuous removal leads to an unstable and fluctuating operation. Hydrophilized cathode flow fields, on the other hand, ensure a stable operation due to removal of excess water by a continuous water film. Two different cell designs including untreated cathode flow fields with either dual-channel or grid design were compared. The grid flow field was superior with regard to the stability of cell performance and less prone to the formation and removal of water droplets. [Copyright &y& Elsevier]