Synchrotron-based X-ray Tomographic Microscopy Research Articles

3D Visualization of Liquid Water Penetration from MPL to Substrate Layer in PEFC Using in-Situ X-Ray Tomographic Microscopy

Polymer electrolyte fuel cells (PEFCs) play an important role in solving environmental problems and energy problems. It is required to perform them at higher current density to achieve the cost reduction. Under the circumstance, however, the cathode gas diffusion layers (GDLs) are saturated with liquid water, which is generated from the electrochemical reaction and condenses. In other words, water is one of the factors that prevents the oxygen diffusion, and clarifying the water management in GDLs is essential to perform at higher current density. At present, synchrotron-based X-ray tomographic microscopy (XTM) is the common way to observe water distribution. While its high intensity makes it possible to get high contrast data by imaging in short exposure time, it decomposes the polymer electrolyte. It is the crucial point to keep cell performance during imaging. In addition, the experiment time using synchrotron radiation facility is limited. To inspect other ways than synchrotron-based XTM, here we aim to achieve 3D visualization of liquid water penetration in GDLs using laboratory-based in-situ XTM. Besides, we aim to evaluate the relationship between water distribution and GDL structure. To get 3D data of liquid water penetration in GDLs using Rigaku nano3DX, which is the laboratory-based X-ray imaging, the fuel cell with an active area 1.0 × 1.0 mm2 was applied. The cell equipped with Toray TGP-H-060 coated with micro porous layer (MPL) was used. 3D data that spatial resolution was 2.16 um was taken. By applying phase retrieval process and image processing, MPL, fiber, water and air were classified. As a result, we have succeeded in the 3D visualization of liquid water penetration from MPL to substrate layer under room temperature. Then, the volume of water captured by XTM was compared with that detected by X-ray radiography to verify that XTM could capture water precisely. This is because some water which is moving during imaging cannot be captured after reconstruction. The total scan time was about 3 hours, which is longer than that of synchrotron-based XTM. It took about 14 second to get an image by X-ray radiography. As a result, though the amount of water near the separator captured by XTM was fewer than that detected by X-ray radiography, the amount of water near MPL and substrate layer was almost the same. The results showed that the liquid water distribution obtained by laboratory-based XTM is reliable. Figure shows 3D images of cathode GDL and water at current density of 0.75, 1.0, 1.25, 1.5 A/cm2. We have identified that water passed through the cracks of MPL and remained in substrate layer where was close to the boundary between MPL and substrate layer. In addition, the effective pore diameter of substrate layer which water remained in was analyzed, and it was identified that water tended to remain in the bigger pore diameter. This is because substrate layer we used is hydrophobic. The result indicates that the existence of cracks on MPL has a strong influence on liquid water distribution and oxygen transport to the catalyst layer. Figure 1

Interface Engineering: On the Impact of Micro-Porous Layers on Polymer Electrolyte Water Electrolysis Performance

In polymer electrolyte water electrolysis (PEWE), operational cost represents the main cost fraction. Losses induced by kinetic, ohmic as well as mass transport overpotentials limit cell efficiency and in turn lead to lower volumetric power density and higher energy consumption.The interplay of porous transport layer bulk/surface properties1,2, providing thermal and electrical conductivity as well as fluid management between bipolar plates and catalyst layer, and cell efficiency is a disputed question in literature. Governing design parameters for porous transport layers, as well as fundamental limiting process haven’t been addressed so far. This study aims to close the gap between fundamentals and highly efficient PTL microstructure design. A novel class of hierarchically structured porous transport layers is fabricated based on sintering of economically viable Ti powder, see Figure 1..A series of four different PTL materials including three different MPL types was analysed. Structural properties, characterized by laboratory and synchrotron based X-ray tomographic microscopy (XTM) were correlated to in-depth electrochemical analysis. Performance of the novel PTLs was probed by comparison to state-of-the-art PTL materials and stack technology. The superior surface properties of the microporous-layer enabled the use of ultra-thin membranes with Ti PTLs for the first time. To elucidate the MPL effect and reveal the mechanism of partial catalyst utilization3,4, the catalyst layer conductivity was studied as function of hydration state and ionomer content.Reference1 S. A. Grigoriev, P. Millet, S. A. Volobuev and V. N. Fateev, International Journal of Hydrogen Energy, 2009, 34, 4968-4973.2 T. Schuler, R. De Bruycker, T. J. Schmidt and F. N. Büchi, Journal of The Electrochemical Society, 2019, 166, F270-F281.3 Z. Kang, J. Mo, G. Yang, S. Retterer, D. Cullen, T. Toops, J. Green Jr, M. Mench and F.-Y. Zhang, Energy and environmental science, 2017, 10, 166-175.4 T. Schuler, T. J. Schmidt and F. N. Büchi, Journal of The Electrochemical Society, 2019, 166, F555-F565.Figure 1. XTM rendering of hierarchically structured porous transport layer. Figure 1

Multi-analytical characterization of Fe-rich magnetic inclusions in diamonds

Magnetic mineral inclusions, as iron oxides or sulfides, occur quite rarely in natural diamonds. Nonetheless, they represent a key tool not only to unveil the conditions of formation of host diamonds, but also to get hints about the paleointensity of the geomagnetic field present at times of the Earth's history otherwise not accessible. This possibility is related to their capability to carry a remanent magnetization dependent on their magnetic history. However, comprehensive experimental studies on magnetic inclusions in diamonds have been rarely reported so far. Here we exploit X-ray diffraction, Synchrotron-based X-ray Tomographic Microscopy and Alternating Field Magnetometry to determine the crystallographic, morphological and magnetic properties of ferrimagnetic Fe-oxides entrapped in diamonds coming from Akwatia (Ghana). We exploit the methodology to estimate the natural remanence of the inclusions, associated to the Earth's magnetic field they experienced, and to get insights on the relative time of formation between host and inclusion systems. Furthermore, from the hysteresis loops and First Order Reversal Curves we determine qualitatively the anisotropy, size and domain state configuration of the magnetic grains constituting the inclusions.

Identification of molybdenite in diamond-hosted sulphide inclusions: Implications for Re–Os radiometric dating

Sulphide inclusions are common features of natural diamonds. They can provide an insight into the nature of diamond-forming reactions and are especially important for Re–Os dating of diamond formation. A discrete molybdenite (MoS2) phase has been identified for the first time by Raman spectroscopy in 73 out of 80 syngenetic sulphide inclusions in 7 eclogitic diamonds from the Mir kimberlite (Yakutia, Russia). The sulphide inclusions were chemically and texturally characterised by electron probe microanalyses (EPMA), focused ion-beam scanning electron microscopy (FIB-SEM) and synchrotron-based X-ray tomographic microscopy (SXRTM). Our observations suggest the molybdenite has unmixed from an original sulphide melt or monosulphide solid solution. It occurs as sub-micron sized grains, commonly in association with the chalcopyrite rims of the inclusions and sometimes, within surrounding decompression cracks. Molybdenite has also been identified by Raman spectroscopy in at least 50% of sulphide inclusions in preliminary studies of eclogitic diamonds from Argyle (NW Australia), Orapa, Letlhakane, Damtshaa (Botswana) and Dachine (French Guiana), and peridotitic diamond-hosted inclusions from Udachnaya (Yakutia, Russia) and Murowa (Zimbabwe). We have modelled the effects that different amounts of Re loss – through its segregation into an unrecovered molybdenite phase – could have on the radiometric ages of diamonds dated using the Re–Os system. In general Re loss through this process will lead to isochron ages older than the true age, and variable degrees of Re loss will lead to increased scatter around the apparent isochron. For model age calculations, the effects would depend on the 187Re/188Os ratio of the inclusions (if their compositions evolved above or below that of the chondritic mantle evolution curve) but Re loss could generate unrealistically old or future ages, particularly in eclogitic inclusions.

Microstructural degradation of silicon electrodes during lithiation observed via operando X-ray tomographic imaging

Due to their high theoretical capacity compared to that of state-of-the-art graphite-based electrodes, silicon electrodes have gained much research focus for use in the development of next generation lithium-ion batteries. However, a major drawback of silicon as an electrode material is that it suffers from particle fracturing due to huge volume expansion during electrochemical cycling, thus limiting commercialization of such electrodes. Understanding the role of material microstructure in electrode degradation will be instrumental in the design of stable silicon electrodes. Here, we demonstrate the application of synchrotron-based X-ray tomographic microscopy to capture and track microstructural evolution, phase transformation and fracturing within a silicon-based electrode during electrochemical lithiation.

Fast iterative reconstruction of data in full interiortomography.

This paper introduces two novel strategies for iterative reconstruction of full interior tomography (FINT) data, i.e. when the field of view is entirely inside the object support and knowledge of the object support itself or the attenuation coefficients inside specific regions of interest are not available. The first approach is based on data edge-padding. The second technique creates an intermediate virtual sinogram, which is, then, reconstructed by a standard iterative algorithm. Both strategies are validated in the framework of the alternate direction method of multipliers plug-and-play with gridding projectors that provide a speed-up of three orders of magnitude with respect to standard operators implemented in real space. The proposed methods are benchmarked on synchrotron-based X-ray tomographic microscopy datasets of mouse lung alveoli. Compared with analytical techniques, the proposed methods substantially improve the reconstruction quality for FINT underconstrained datasets, facilitating subsequent post-processing steps.

X-rays and virtual taphonomy resolve the first Cissus (Vitaceae) macrofossils from Africa as early-diverging members of the genus.

Fossilized seeds similar to Cissus (Vitaceae) have been recognized from the Miocene of Kenya, though some were previously assigned to the Menispermaceae. We undertook a comparative survey of extant African Cissus seeds to identify the fossils and consider their implications for the evolution and biogeography of Cissus and for African early Miocene paleoenvironments. Micro-computed tomography (µCT) and synchrotron-based X-ray tomographic microscopy (SRXTM) were used to study seed morphology and anatomy. Virtual taphonomy, using SRXTM data sets, produced digital fossils to elucidate seed taphonomy. Phylogenetic relationships within Cissus were reconstructed using existing and newly produced DNA sequences for African species. Paleobiology and paleoecology were inferred from African nearest living relatives. The fossils were assigned to four new Cissus species, related to four modern clades. The fossil plants were interpreted as climbers inhabiting a mosaic of riverine woodland and forest to more open habitats. Virtual taphonomy explained how complex mineral infill processes concealed key seed features, causing the previous taxonomic misidentification. Newly sampled African species, with seeds most similar to the fossils, belong to four clades within core Cissus, two of which are early diverging. Virtual taphonomy, combined with X-ray imaging, has enabled recognition of the first fossil Cissus and Vitaceae from Africa. Early-divergent members of the core Cissus clade were present in Africa by at least the early Miocene, with an African origin suggested for the Cissus sciaphila clade. The fossils provide supporting evidence for mosaic paleoenvironments inhabited by early Miocene hominoids.

Comparison of three‐dimensional analysis and stereological techniques for quantifying lithium‐ion battery electrode microstructures

SummaryLithium‐ion battery performance is intrinsically linked to electrode microstructure. Quantitative measurement of key structural parameters of lithium‐ion battery electrode microstructures will enable optimization as well as motivate systematic numerical studies for the improvement of battery performance. With the rapid development of 3‐D imaging techniques, quantitative assessment of 3‐D microstructures from 2‐D image sections by stereological methods appears outmoded; however, in spite of the proliferation of tomographic imaging techniques, it remains significantly easier to obtain two‐dimensional (2‐D) data sets. In this study, stereological prediction and three‐dimensional (3‐D) analysis techniques for quantitative assessment of key geometric parameters for characterizing battery electrode microstructures are examined and compared. Lithium‐ion battery electrodes were imaged using synchrotron‐based X‐ray tomographic microscopy. For each electrode sample investigated, stereological analysis was performed on reconstructed 2‐D image sections generated from tomographic imaging, whereas direct 3‐D analysis was performed on reconstructed image volumes. The analysis showed that geometric parameter estimation using 2‐D image sections is bound to be associated with ambiguity and that volume‐based 3‐D characterization of nonconvex, irregular and interconnected particles can be used to more accurately quantify spatially‐dependent parameters, such as tortuosity and pore‐phase connectivity.

Operando X-ray Tomographic Microscopy Imaging of HT-PEFC: A Comparative Study of Phosphoric Acid Electrolyte Migration

Synchrotron based X-ray tomographic microscopy was used to image the redistribution of phosphoric acid in HT-PEFC due to electrolyte migration from cathode to anode. The acid migration rate, transference number of the hydrogen phosphate ion and flooding of the anode gas diffusion layer (GDL) was analyzed for MEAs with different membrane acid doping levels (24–36 mgcm−2) and membrane materials (imbibed m-polybenzimidazole (PBI) and polyphosphoric acid (PPA) processed p-PBI). The most influential factors for the acid migration rate are current density and the amount of free acid in the membrane. High doping level of the membrane and current density above 0.4 A cm−2 significantly increase the migration rate. From the migration rates apparent transference numbers for the hydrogen phosphate anions in the order 10−5 to 10−4 are calculated at the high current densities. Besides the membrane properties, also the influence of the microstructure of the porous transport layers was analyzed. Most probably cracks in the catalyst and microporous layers facilitate the migration of acid into the anode GDL.

In situ X-ray tomographic microscopy observations of vesiculation of bubble-free and bubble-bearing magmas

Magma degassing is thought to play a major role in magma fractionation, transport, storage, and volcanic eruption dynamics. However, the conditions that determine when and how magma degassing operates prior to and during an eruption remain poorly constrained. We performed experiments to explore if the initial presence of gas bubbles in magma influences the capability of gas to escape from the magma. Vesiculation of natural H2O-poor (<<1 wt.%) silicic obsidian glasses was investigated by in situ, high-temperature (above the glass transition) experiments using synchrotron-based X-ray tomographic microscopy with high spatial (3 μm/pixel) and temporal resolution (1 second per 3D dataset). As a validation, a second set of experiments was performed on identical starting materials using a Karl-Fisher titration setup to quantify the amount of extracted gas that escapes via volatile diffusion and/or bubble coalescence during vesiculation. In both sets of experiments, vesiculation was triggered by heating the samples at room pressure. Our results suggest that the presence of pre-existing gas bubbles during a nucleation event significantly decreases the tendency of bubbles to coalesce and inhibits magma outgassing. In contrast, in initially bubble-free samples, the nucleation and growth of bubbles is accompanied by significant coalescence and outgassing. We infer that volatile-undersaturated (i.e. bubble-free) magmas in the reservoirs are more likely to erupt effusively, while the presence of excess gas already at depth (i.e. bubble-bearing systems) increases the likelihood of explosive eruptions.

Seed morphology and anatomy and its utility in recognizing subfamilies and tribes of Zingiberaceae.

Recent phylogenetic analyses based on molecular data suggested that the monocot family Zingiberaceae be separated into four subfamilies and four tribes. Robust morphological characters to support these clades are lacking. Seeds were analyzed in a phylogenetic context to test independently the circumscription of clades and to better understand evolution of seed characters within Zingiberaceae. Seventy-five species from three of the four subfamilies were analyzed using synchrotron based x-ray tomographic microscopy (SRXTM) and scored for 39 morphoanatomical characters. Zingiberaceae seeds are some of the most structurally complex seeds in angiosperms. No single seed character was found to distinguish each subfamily, but combinations of characters were found to differentiate between the subfamilies. Recognition of the tribes based on seeds was possible for Globbeae, but not for Alpinieae, Riedelieae, or Zingibereae, due to considerable variation. SRXTM is an excellent, nondestructive tool to capture morphoanatomical variation of seeds and allows for the study of taxa with limited material available. Alpinioideae, Siphonochiloideae, Tamijioideae, and Zingiberoideae are well supported based on both molecular and morphological data, including multiple seed characters. Globbeae are well supported as a distinctive tribe within the Zingiberoideae, but no other tribe could be differentiated using seeds due to considerable homoplasy when compared with currently accepted relationships based on molecular data. Novel seed characters suggest tribal affinities for two currently unplaced Zingiberaceae taxa: Siliquamomum may be related to Riedelieae and Monolophus to Zingibereae, but further work is needed before formal revision of the family.

A Fungal-Prokaryotic Consortium at the Basalt-Zeolite Interface in Subseafloor Igneous Crust.

We have after half a century of coordinated scientific drilling gained insight into Earth´s largest microbial habitat, the subseafloor igneous crust, but still lack substantial understanding regarding its abundance, diversity and ecology. Here we describe a fossilized microbial consortium of prokaryotes and fungi at the basalt-zeolite interface of fractured subseafloor basalts from a depth of 240 m below seafloor (mbsf). The microbial consortium and its relationship with the surrounding physical environment are revealed by synchrotron-based X-ray tomographic microscopy (SRXTM), environmental scanning electron microscopy (ESEM), and Raman spectroscopy. The base of the consortium is represented by microstromatolites—remains of bacterial communities that oxidized reduced iron directly from the basalt. The microstromatolites and the surrounding basalt were overlaid by fungal cells and hyphae. The consortium was overgrown by hydrothermally formed zeolites but remained alive and active during this event. After its formation, fungal hyphae bored in the zeolite, producing millimetre-long tunnels through the mineral substrate. The dissolution could either serve to extract metals like Ca, Na and K essential for fungal growth and metabolism, or be a response to environmental stress owing to the mineral overgrowth. Our results show how microbial life may be maintained in a nutrient-poor and extreme environment by close ecological interplay and reveal an effective strategy for nutrient extraction from minerals. The prokaryotic portion of the consortium served as a carbon source for the eukaryotic portion. Such an approach may be a prerequisite for prokaryotic-eukaryotic colonisation of, and persistence in, subseafloor igneous crust.

High-throughput phenotyping and genetic linkage of cortical bone microstructure in the mouse.

BackgroundUnderstanding cellular structure and organization, which plays an important role in biological systems ranging from mechanosensation to neural organization, is a complicated multifactorial problem depending on genetics, environmental factors, and stochastic processes. Isolating these factors necessitates the measurement and sensitive quantification of many samples in a reliable, high-throughput, unbiased manner. In this manuscript we present a pipelined approach using a fully automated framework based on Synchrotron-based X-ray Tomographic Microscopy (SRXTM) for performing a full 3D characterization of millions of substructures.ResultsWe demonstrate the framework on a genetic study on the femur bones of in-bred mice. We measured 1300 femurs from a F2 cross experiment in mice without the growth hormone (which can confound many of the smaller structural differences between strains) and characterized more than 50 million osteocyte lacunae (cell-sized hollows in the bone). The results were then correlated with genetic markers in a process called quantitative trait localization (QTL). Our findings provide a mapping between regions of the genome (all 19 autosomes) and observable phenotypes which could explain between 8–40 % of the variance using between 2–10 loci for each trait. This map shows 4 areas of overlap with previous studies looking at bone strength and 3 areas not previously associated with bone.ConclusionsThe mapping of microstructural phenotypes provides a starting point for both structure-function and genetic studies on murine bone structure and the specific loci can be investigated in more detail to identify single gene candidates which can then be translated to human investigations. The flexible infrastructure offers a full spectrum of shape, distribution, and connectivity metrics for cellular networks and can be adapted to a wide variety of materials ranging from plant roots to lung tissue in studies requiring high sample counts and sensitive metrics such as the drug-gene interactions and high-throughput screening.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1617-y) contains supplementary material, which is available to authorized users.

Evolutionary significance of seed structure in Alpinioideae (Zingiberaceae)

Alpinioideae is the largest of the four subfamilies of Zingiberaceae and is widely distributed throughout the New and Old World tropics. Recent molecular studies have shown that, although Alpinioideae is a strongly supported monophyletic subfamily with two distinct tribes (Alpinieae and Riedelieae), large genera, such as Alpinia and Amomum, are polyphyletic and are in need of revision. Alpinia and Amomum have been shown to form seven and three distinct clades, respectively, but, for many of these clades, traditional vegetative and floral synapomorphies have not been found. A broad survey of seeds in Alpinioideae using light microscopy and synchrotron-based X-ray tomographic microscopy has shown that many clades have distinctive seed structures that serve as distinctive apomorphies. Tribes Riedelieae and Alpinieae can be distinguished on the basis of operculum structure, with the exception of three taxa analysed. The most significant seed characters were found to be various modifications of the micropylar and chalazal ends, the cell shape of the endotesta and exotesta, and the location of an endotestal gap. A chalazal chamber and hilar rim are reported for the first time in Zingiberaceae. In addition to characterizing clades of extant lineages, these data offer insights into the taxonomic placement of many fossil zingiberalean seeds that are critical to understanding the origin and evolution of Alpinioideae and Zingiberales as a whole.

Dynamic Operation of HT-PEFC: In-Operando Imaging of Phosphoric Acid Profiles and (Re)distribution

Synchrotron based X-ray tomographic microscopy (XTM) is used for imaging and quantifying the redistribution of phosphoric acid (PA) in high temperature polymer electrolyte fuel cells (HT-PEFC) in-operando. The main focus of this work is the redistribution of phosphoric acid under dynamic load conditions. Therefore, two different load cycling protocols were applied and the transient redistribution within the fuel cell components was imaged. XTM, for the first time, revealed that the examined PBI based membrane system exhibits extensive electrolyte migration from cathode to anode under high current density operation. PA flooding of anode gas diffusion layer (GDL) and flow field channels occurred. Implications for technical applications and fuel cell degradation are discussed. Quantification of the migrated electrolyte is made by correlating in-operando grayscale values to ex-situ reference samples.

Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy.

Synchrotron-based X-ray tomographic microscopy is investigated for imaging the local distribution and concentration of phosphoric acid in high-temperature polymer electrolyte fuel cells. Phosphoric acid fills the pores of the macro- and microporous fuel cell components. Its concentration in the fuel cell varies over a wide range (40-100 wt% H3PO4). This renders the quantification and concentration determination challenging. The problem is solved by using propagation-based phase contrast imaging and a referencing method. Fuel cell components with known acid concentrations were used to correlate greyscale values and acid concentrations. Thus calibration curves were established for the gas diffusion layer, catalyst layer and membrane in a non-operating fuel cell. The non-destructive imaging methodology was verified by comparing image-based values for acid content and concentration in the gas diffusion layer with those from chemical analysis.

Synchrotron-based X-ray tomographic microscopy for visualization of three-dimensional collagen matrices.

Three-dimensional collagen matrices (3D-CMs) may be visualized by cumbersome reconstructions of serial sections. We report here on the method of synchrotron-based X-ray tomographic microscopy (SRXTM) to image 3D-CMs in native tissue probes. SRXTM of 3D-CMs (mucoderm®, mucograft®) was performed at the TOMCAT beamline of the Swiss Light Source (SLS) at the Paul Scherrer Institute (Villigen, Switzerland). SRXTM combines the advantages of high-resolution scanning electron microscopy (SEM) imaging with the low-resolution reconstructions of micro-CT (μCT) imaging. It may be used to non-destructively visualize and analyze structures within the 3D-CMs without the need of serial sectioning and reconstruction. High-resolution SRXTM is a useful tool in analyzing the topology and morphometry of structures in 3D-CMs. The outcome justifies the efforts in sophisticated data processing. SRXTM may help to understand the clinical characteristics of 3D-CMs in more detail.

Gas Cross-over and Durability of Membrane Electrode Assemblies

Durability of the membrane electrolyte is a key factor for the longevity of polymer electrolyte fuel cells. A loss of gas separation is the most detrimental failure mode of perfluorosulfonic acid membranes. Mechanical formation of micron sized membrane defects is the main degradation process during fuel cell operation. This process is accelerated by variations in the operating conditions, such as humidity and temperature, and by imperfections and local defects of the gas diffusion electrodes.The impact of these local defects, termed pinholes is studied by implementing artificial micron sized defects in the membrane by focused ion beam (FIB) milling. Such membranes were then operated in different accelerated stress tests to study the development of chemical, mechanical and thermal degradation processes. Degradation at membrane defects was investigated post mortem using synchrotron based X-ray tomographic microscopy (XTM) and FTIR spectro-microscopy (see Figure 1) [1]. Gas cross-over, a key function for degradation, is controlled by operating conditions and material characteristics and was measured in-situ by mass spectrometry using a tracer gas concept [2, 3].From the results an overall degradation mechanism at membrane defects can be thus formulated [4].[1] S. Kreitmeier, M. Michiardi, A. Wokaun, F. N. Büchi, Factors determining the gas crossover through pinholes in polymer electrolyte fuel cell membranes, Electrochim. Acta, 80, 240-247 (2012)[2] G. A. Schuler, A. Wokaun, F. N. Büchi, Local online gas analysis in PEFC using tracer gas concepts, J. Power Sources, 195, 1647–1656 (2010)[3] S. Kreitmeier, G. A. Schuler, A. Wokaun, F. N. Büchi, Investigation of membrane degradation in polymer electrolyte fuel cells using local gas permeation analysis, J. Power Sources, 212, 139-147(2012)[4] S. Kreitmeier, P. Lerch, A. Wokaun, F.N. Büchi, Local degradation at membrane defects in polymer electrolyte fuel cells, J. Electrochem. Soc. 160, F456-F463 (2013)

The dynamics of interfaces during coarsening in solid–liquid systems

The isothermal coarsening of dendritic Al–Cu microstructures is examined using time-resolved, in situ synchrotron-based X-ray tomographic microscopy. By obtaining the data at the coarsening temperature (in situ) with speeds that are on the order of or faster than the ongoing evolution of the microstructure (time-resolved, 4-D), we examine the dynamic morphological evolution of the solid–liquid interfaces in two solid volume fractions; as such, the relationship between the velocity of the evolving interface and characteristics that define the morphology of the interface is determined. We find that, while there is a correlation between velocity and mean curvature of the interface, there is a significant dispersion in the velocities for a given value of mean curvature. In addition, the Gaussian curvature plays a role in determining the interface velocity even though it has no effect on the chemical potential at the interface. We find that there are many interface patches of various morphologies and size scales that are not evolving during the coarsening process. At higher solid volume fractions and longer coarsening times, more of the structure is active in the coarsening process, and there is an increase in localized diffusional interactions.

Coupling in situ synchrotron X-ray tomographic microscopy and numerical simulation to quantify the influence of intermetallic formation on permeability in aluminium–silicon–copper alloys

The influence of the β-Al5FeSi intermetallic phase on permeability evolution during solidification in an Al–Si–Cu alloy with a columnar dendritic microstructure has been numerically studied at solid fractions between 0.10 and 0.85. The fluid flow simulations were performed on a semisolid microstructure extracted directly from a single solidifying specimen, enabling the first study of permeability variation on an individual microstructure morphology that is evolving in solid fraction. The 3-D geometries were imaged at the TOMCAT beamline using 4-D (3-D+time) in situ synchrotron-based X-ray tomographic microscopy. The results illustrate the major effect of intermetallic particles on flow blockage and permeability. Intermetallics that grow normal to the flow direction were found to have a greater impact on the flow field in comparison to intermetallics in the parallel flow direction. An analytical expression, based on the anisotropic Blake–Kozeny model, was developed with a particle blockage term that takes into account the effects of intermetallic particles on permeability. In the regime of primary-phase solidification, a good fit between the analytical expression and the simulation results is found.