The aim of the present investigation is to define microstructure parameters, which control the effective transport properties in porous materials for energy technology. Recent improvements in 3D-imaging (FIB-nanotomography, synchrotron X-ray tomography) and image analysis (skeletonization and graph analysis, transport simulations) open new possibilities for the study of microstructure effects. In this study, we describe novel procedures for a quantitative analysis of constrictivity, which characterizes the so-called bottleneck effect. In a first experimental part, methodological tests are performed using a porous (La,Sr)CoO 3 material (SOFC cathode). The tests indicate that the proposed procedure for quantitative analysis of constrictivity gives reproducible results even for samples with inhomogeneous microstructures (cracks, gradient of porosity). In the second part, 3D analyses are combined with measurements of ionic conductivity by impedance spectroscopy. The investigations are preformed on membranes of electrolysis cells with porosities between 0.27 and 0.8. Surprisingly, the tortuosities remain nearly constant (1.6) for the entire range of porosity. In contrast, the constrictivities vary strongly and correlate well with the measured transport resistances. Hence, constrictivity represents the dominant microstructure parameter, which controls the effective transport properties in the analysed membrane materials. An empirical relationship is then derived for the calculation of effective transport properties based on phase volume fraction, tortuosity, and constrictivity.

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[1] Local porosity theory in combination with percolation theory was applied to shale microstructures that were reconstructed on the basis of focused ion beam nanotomography and scanning transmission electron microscopy. This allowed characterizing pore microstructures in Opalinus clay with length scales on the order of tens of microns. In a sample from the sandy facies (with low clay content), the fraction of "larger" pores f(radii~> 15 nm) = 0.076 is substantially higher than that in the shaley facies (with a higher clay content), where f(radii~> 15 nm) = 0.015. The resolved porosity possesses a certain degree of homogeneity, and the representative volume element (RVE) of porosity can be determined in terms of a given relative error on porosity. For example, if we accept a relative error of 10%, the RVE is on the scale of a few hundreds of microns. Both pore microstructures from sandy and shaley facies show anisotropic characteristics with respect to connectivity and percolation threshold. Using finite scaling, we found percolation thresholds with critical porosities f c,b = 0.04-0.12 parallel to bedding and f c,perp = 0.11-0.19 perpendicular to bedding. The resolved porosity of the sandy facies (low clay content) is close to the percolation threshold, whereas the porosity of the shaley facies (high clay content) is below the percolation threshold. The porosity in carbonate layers is around f = 0.027, and the pore size is substantially larger when compared to the pores in the clay matrix. In the analyzed sample, pores in carbonate layers are poorly connected.Citation: Keller, L. M., L. Holzer, P. Schuetz, and P. Gasser (2013), Pore space relevant for gas permeability in Opalinus clay: Statistical analysis of homogeneity, percolation and representative volume element,

The ion conductivity of two series of porous ceramic diaphragms impregnated with caustic potash was investigated by electrochemical impedance spectroscopy. To understand the impact of the pore structure on ion conductivity, the threedimensional (3-D) pore geometry of the diaphragms was characterized with synchrotron x-ray absorption tomography. Ion migration was calculated based on an extended pore structure model, which includes the electrolyte conductivity and geometric pore parameters, for example, tortuosity (s) and constriction factor (b), but no fitting parameters. The calculated ion conductivities are in agreement with the data obtained from electrochemical measurements on the Correspondence concerning this article should be addressed to D. Wiedenmann at daniel.wiedenmann@gmail.com.Published in " " which should be cited to refer to this work.http://doc.rero.ch diaphragms. The geometric tortuosity was found to be nearly independent of porosity. Pore path constrictions diminish with increasing porosity. The lower constrictivity provides more pore space that can effectively be used for mass transport. Direct measurements from tomographs of tortuosity and constrictivity opens new possibilities to study pore structures and transport properties of porous materials.

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This study analyses the mineralogical and chemical transformations associated with an Alpine shear zone in polymetamorphic metapelites from the Monte Rosa nappe in the upper Val Loranco (N-Italy). In the shear zone, the pre-Alpine assemblage plagioclase + biotite + kyanite is replaced by the assemblage garnet + phengite + paragonite at eclogite facies conditions of about 650°C at 12.5 kbar. Outside the shear zone, only minute progress of the same metamorphic reaction was attained during the Alpine metamorphic overprint and the pre-Alpine mineral assemblage is largely preserved. Textures of incomplete reaction, such as garnet rims at former grain contacts between preexisting plagioclase and biotite, are preserved in the country rocks of the shear zone. Reaction textures and phase relations indicate that the Alpine metamorphic overprint occurred under largely anhydrous conditions in low strain domains. In contrast, the mineralogical changes and phase equilibrium diagrams indicate water saturation within the Alpine shear zones. Shear zone formation occurred at approximately constant volume but was associated with substantial gains in silica and losses in aluminium and potassium. Changes in mineral modes associated with chemical alteration and progressive deformation indicate that plagioclase, biotite and kyanite were not only consumed in the course of the garnet-and phengite-producing reactions, but were also dissolved ÔcongruentlyÕ during shear zone formation. A large fraction of the silica liberated by plagioclase, biotite and kyanite dissolution was immediately re-precipitated to form quartz, but the dissolved aluminium-and potassium-bearing species appear to have been stable in solution and were removed via the pore fluid. The reaction causes the localization of deformation by producing fine-grained white mica, which forms a mechanically weak aggregate.

Structural and metamorphic evolution SW of the Simplon line 19 ABSTRACT This structural and petrological study examines relationships between Alpine deformation and metamorphism in the Camughera-Moncucco, Antrona and northeastern Monte Rosa units, and it correlates major late stage deformation structures, such as the Vanzone antiform and Simplon normal fault. D1/D2 deformation and related top-N or top-NW thrusting started under high-pressure conditions (12.5-16 kbar) at relatively high temperatures (c. 620-700°C). Petrological and structural data, together with published radiometric data, suggest that top-SE shearing within the structural top of the high-pressure units in the upper Penninic Alps is coeval with top-N or top-NW thrusting at their structural base. This suggests differential ascent of high-pressure units relative to the surrounding units during nappe stacking and associated crustal shortening. Barrovian metamorphism in the upper Penninic Alps is related to a first phase of backfolding, active between c. 35 Ma and c. 29-26 Ma ago (D3). D3 involves dextral shearing, combined with top-WSW shearing and orogen-parallel extension. Unroofing by orogen-parallel extension delays cooling during decompression and leads to isothermal decompression after the high-pressure stage. Towards deeper structural levels in the east, D3 deformation becomes progressively younger and prevailed at increasingly higher temperatures. Hence, compared to the higher structural levels further west, the brittle-ductile transition occurs later in the Ossola valley. Masera synform and Brevettola antiform form an open fold pair and represent the eastern continuation of the major Vanzone antiform (D4). Normal faulting across the Simplon line overlaps in time with the formation of these major D4 backfolds. Displacement along the Simplon normal fault decreases to insignificant values towards the southeast. Contemporaneous dextral shearing, however, occurs within the southern limbs of the Vanzone and Brevettola antiforms. ZUSAMMENFASSUNGDiese strukturelle und petrologische Arbeit untersucht die Beziehungen zwischen alpiner Deformation und Metamorphose in den Camughera-Moncucco und Antrona Einheiten sowie in der nordöstlichen Monte Rosa Decke. Zusätzlich werden grossräumige spätalpine Strukturelemente, wie die Vanzone Antiform und die Simplon Abschiebung, in einen Zusammenhang gebracht. Die D1/D2 Deformationsphase ist mit nach N oder NW gerichteten Über-schiebungen assoziiert, welche anfänglich unter Hochdruckbedingungen (12.5-16 kbar) und relativ hohen Temperaturen (c. 620-700°C) aktiv waren. Petrologische und strukturelle Daten, sowie publizierte radiometrische Daten, vermuten, dass SE gerichtete Abschiebungen im oberen Teil der penninischen Hochdruckeinheiten gleichzeitig mit nach NW gerichteten Überschiebungen an deren Basis aktiv waren. Dies legt es nahe, dass die Hochdruckeinheiten während der Deckenbildung und Krustenverkürzung relativ zu den umgebenden Einheiten differentiell aufgestiegen sind. Die Metamorphose vom Barrow-Typ in den ...