Microscopy Conference 2023

Session chairs

In this session, we invite contributions across a variety of disciplines, from all areas of geosciences, such as environmental pollution redemption to ore deposits and deep earth, planetary or extraterrestrial samples over construction materials such as cement and concrete to the study of objects of cultural heritage. We hope to connect these very diverse but highly innovative and exiting research areas by focusing the discussions on our common interest on processes on the nm-scale, particularly where interfaces are involved, from mineralization, crystallization to nucleation, growth, diffusion, deformation and phase transformations.

Prof.

Stress-induced amorphization and grain boundary sliding in olivine

Abstract text (incl. figure legends and references) (Mg, Fe)2SiO4 olivine is the most volumetric abundant mineral phase in the upper mantle down to 410 km depth and also the one which deforms the most and controls the rheology of the upper mantle. Deformation mechanisms in olivine have attracted considerable attention since several decades. One of the problems with this orthorhombic mineral is that there are not enough slip systems to produce a general deformation. The observation of a non-linear deformation regime depending on the grain size has led to the suggestion of the possibility of slip at the grain boundary [1], which has only recently been demonstrated microstructurally [2]. In this paper we show that under high stresses, this grain boundary sliding can be due to the amorphization of the grain boundary and to the flow of this amorphous intergranular phase. We show how nanomechanical testing in situ in the TEM allows to characterize this individual mechanism as well as the rheology of this amorphous olivine. We finally propose that this mechanism of stress-induced amorphization is an important deformation mechanism in its own right under conditions of high stress [3]. [1] Hirth, G., &amp; Kohlstedt, D. (1995) Experimental constraints on the dynamics of the partially molten upper mantle: 2. Deformation in the dislocation creep regime, Journal of Geophysical Research, 100, 15,441–15,449, [2] Bollinger, C., Marquardt, K. &amp; Ferreira, F. (2019) Intragranular plasticity vs. grain boundary sliding (GBS) in forsterite: microstructural evidence at high pressures (3.5–5.0 GPa). American Mineralogist 104, 220–231. [3] Idrissi, H., Carrez, P., &amp; Cordier, P. (2022) On amorphization as a deformation mechanism under high stresses. Current Opinion in Solid State &amp; Materials Science. 26(1), 100976

MS 6: Geoscience and construction materials, cultural heritage

MS 7: Ceramics and composites

Invited talk

Nucleation mechanism of Magnesium-Silicate-Hydrate (M-S-H) cement

Abstract text (incl. figure legends and references) Concrete is the most used artificial material of humankind. But despite the importance of concrete to our infrastructure, the production of its binder cement is contributing to a significant amount of the global CO2 emissions. [1] Actions to reduce cement&quot;s massive carbon footprint involve strategies that include the utilization of abundant clays and minerals but also the development of low carbon binders. [2] Magnesium-Silicate-Hydrate (M-S-H) has caught the attention of material scientists as an alternative binder that could be produced from low carbon resources like seawater brines and the extraction of educts from abundant minerals like olivine. [2-3] Until now, most alternative binders are only scarcely researched and suffer from deficient material properties compared to traditional Portland cement. Innovative binders must meet certain requirements, such as being environmentally friendly, sustainable, having suitable material properties while also being economically reasonable. Fundamental knowledge about the nucleation and growth mechanisms will be pivotal to control the formation and nanostructure of the cementitious material from the bottom up, via the use of designed polymeric or mineral additives formulations. Herein, we investigate first the early stages of M-S-H formation in an additive-free enviroment with physicochemical methods like analytical ultracentrifugation (AUC) coupled with ESI-MS and time-resolved potentiometric titration. This enable us to decipher the moieties present in the pre-nucleation phase and how they affect the postnucleation phase of theM-S-H. Characterization of the final product involves multiple state-of-the-art techniques used in the analysis of morphology and composition (TEM, SEM, IR, XRD). [1] J. Lehne, F. Preston, Chatham House Report, Energy Enivronment and Resources Department: London, UK 2018, 1-66. [2] E. Gartner, T. Sui, cement and concrete research 2018, 114, 27-39. [3] S. Allan Nye, S. Vineet, O. Christopher, S. Barnaby, C. Chris, Frontiers in Built Environment 2021, 7.

Prof. Dr.

Dr.-Ing.

Phase separation of olivine in basalt aggregate induced by fatigue damage of ultra-high performance concrete

Abstract text (incl. figure legends and references) Introduction Ultra-high performance concrete (UHPC), a specialized form of concrete characterized by its high compressive strength of up to 200 N/mm2, has garnered considerable interest since the first reports in the early 1990s.[1] Today, it is used mostly in structures with high strength requirements such as bridges, high-rise buildings and wind turbine towers. Objectives Due to the high cement content of fine-grained UHPC, its production entails the emission of large amounts of CO2. In an attempt to mitigate this effect, we try to introduce conventional coarse aggregate from suitable high-strength rocks such as basalt or granite into the formula. However, the average and maximum lifetime of specimens during cyclic loading tests significantly decreases compared to UHPC not containing any coarse aggregate. One of our aims is to investigate the origins of this phenomenon using electron microscopy methods. Materials and methods UHPC was fabricated with ordinary Portland cement (CEM I), a water-to-cement ratio (w/c) of 0.24, quartz sand (maximum grain size ca. 500 µm) and quartz powder (20 µm) as aggregate, nanoscale silica fume and a PCE superplasticizer. Additionally, up to 30 vol.-% of basalt gravel (grain size 2 to 8 mm) were used as coarse aggregate. After hardening for at least 56 days, cylindrical samples were subjected to cyclic uniaxial compressive loading between lower and upper limits of 5 and 80%, respectively, of the short-term compressive strength. We performed testing until failure or until a desired point on the lifetime curve was reached. From whole specimens or suitable fragments, samples were extracted via mechanical as well as focused ion beam (FIB) methods and investigated using SEM, TEM and EDS spectral imaging. Results The basalt we used is a volcanic rock comprised of phenograins with a size of ca. 100 to 200 µm of mostly pyroxene (augite and jadeite), olivine and titanomagnetite embedded in a feldspar groundmass. Figure 1: Large-area EDS map of basalt. Additionally, we observe small phenograins of chloroapatite. Among olivine grains, most are affected by weathering in the shape of numerous cracks often permeating the entire grain. While this phenomenon has been known for decades,[2] we observe the conversion becoming more pronounced with progressing fatigue damage from cyclic loading. Cracks grow in width from 2 to 4 µm in the pristine state to up to 40 µm in post-failure specimens. Using EDS elemental mapping, we find a phase separation of olivine (magnesium iron silicate) into two or more separate compounds. Most cracks exhibit a distinct structure with an iron-rich outer region bordering the unaffected olivine mineral and a zigzag-shaped inner region rich in magnesium and silicon. In the very center of each crack, we observe enrichments of trace elements elements not commonly found in olivine such as aluminum and occasionally calcium, nickel or sulfur. Figure 2: BSE-SEM image and EDS maps of phase separation in olivine. Conclusion We conclude that trace elements in olivine accumulate at interfaces. In the event of mechanical fatigue, inner friction occurs at these interfaces, resulting in a local rise in temperature that enables and promotes a phase separation of the mineral. References [1] D. H. Wang et al., Const. Build. Mater. 2015, 96, 368-377. [2] W. A. Deer, R. A. Howie, J. Zussman, An Introduction to the Rock-Forming Minerals, 3rd edition, Longmans, London, 2013.

Abstract talk

Alteration of Illite by Bad Nauheimer and Gerolsteiner Brine: implications on fluid permeability in geothermal projects

Abstract text (incl. figure legends and references) Illite is one of the most abundant clay minerals on earth, yet its structure remains not fully resolved. Illites of the Remlinger sandstone display a fibrous growth around the detrital grains and form a meshwork within the pores of the sandstone. The meshwork and particles trapped therein during fluid flow lead to a dramatic decrease in permeability, which should be prevented in geothermal systems using for example such sandstones. In autoclave experiments, the interaction of the Remlinger sandstone with two different natural brines, Bad Nauheimer and Gerolsteiner, were compared to an unaltered sandstone as reference, in order to determine possible changes in structure, stacking or shape of the illite fibers. The surface of fluid-altered sandstone plugs was characterized using environmental scanning microscopy (ESEM). Grinded material of rim and core was examined by X-ray powder diffraction (XRPD). In addition, particles filtered from the fluid after the autoclave experiment were investigated employing transmission electron microscopy (TEM). Moreover, 3D electron diffraction experiments were performed using Automated Diffraction Tomography (ADT) (Kolb U., 2012; Rozhdestvenskaya et al., 2011). Based on a 50 nm illite fiber, the structure of illite could be solved during TEM analysis using a single ADT data set. The reconstructed reciprocal space also revealed one-dimensional diffuse scattering, indicating a disorder in the stacking of the illite layers. The degree of disorder is dependent on the potassium content of the fluid, since the K+-ions of the interlayer can be released via the (010) habit plane. This reduces the stability of the structure, resulting in a high fragmentation and detachment of individual illite layers. Such mobile layer fragments can then be transported by mobile fluids to interact and entangle in the sandstone. These new insights into the structure of illite fibers show a distinct dependence of the arrangement and local agglomeration of the fibers in the pores on the potassium content of the fluid (brine) used. The increased migration and interweaving of the fibers associated with a low potassium content can lead to severe clogging of the pores and thus to a reduction in fluid permeability. Altered sandstones with illitic pore filling are therefore less suitable for long-term geothermal projects. Kolb U. 2012: Automated Diffraction Tomography. Uniting Electron Crystallography and Powder Diffraction. Springer, 314-326. Rozhdestvenskaya E., Mugnaioli E., Czank M., Depmeier W., Kolb U., Merlino S. 2011: Essential Features of the Polytypic Charoite-96 Structure Compared to Charoite-90. Mineral. Magazine, 75, No. 6, 2833-2846.

IM 5: Quantitative image and diffraction data analysis

Strain hardening in garnet during deep crustal earthquakes

Abstract text (incl. figure legends and references) Mechanical models of the lithosphere assume a brittle upper layer and a ductile middle to lower layer separated by a steady-state transition occurring at a depth of ~15 km. Consequently, earthquakes typically occur in the upper continental crust1. Seismicity indicators such as pseudotachylytes in deeply exhumed rocks, however, evince earthquakes also occur in the lower crust (&gt;50 km)2. Under these high-temperature conditions, rocks are expected to behave ductily therefore post-seismic ductile creep commonly obscures microstructures associated with seismic events in most crust-forming minerals3. Thus, the mechanics of seismic failure in the deeper crust remain largely unknown. Garnet, however, is a high-strength mineral and preserves structures that can be used to understand the rheological behaviour of the lower crust4. Herein, we study garnet porphyroclasts from an eclogite facies mylonite in the Musgrave province (central Australia) to investigate the mechanisms by which garnet is deformed under dry, lower crustal conditions. Our correlated microscopy approach combines 2D and 3D structural and geochemical analytical techniques including electron backscatter diffraction (EBSD), high-contrast backscatter electron (BSE) imaging, and atom probe tomography (APT). EBSD mapping and BSE imaging reveal bands of small, strain-free grains with scattered orientations, outlined by polygonal to lobate high-angle grain boundaries crosscutting the porphyroclasts in the vicinity of fractures. APT analysis of a high-angle grain boundary shows Fe enrichment in the form of planar and nearly equally spaced arrays of Fe-rich nanoclusters. The combined results demonstrate Fe segregation along grain boundaries of recrystallized garnet, resulting in the nucleation of Fe-rich clusters that can act as barriers for migrating dislocations and lead to strain-hardening and facilitate brittle fracture. Our findings potentially contribute to the mechanisms of mechanical failure in the lower continental crust that lead to deep seismicity. 1Green, H., Houston, H., 1995, The mechanics of deep earthquakes: Annual Review of Earth and Planetary Sciences, v. 23, p. 169–213. 2Austrheim, H., and Boundy, T., 1994, Pseudotachylytes generated during seismic faulting and eclogitization of the deep crust: Science, v. 265, p. 82–83. 3Kirkpatrick, J., and Rowe, C., 2013, Disappearing ink: How pseudotachylytes are lost from the rock record: Journal of Structural Geology, v. 52, p. 183–198. 4Mancktelow, N., Camacho, A., and Pennacchioni, G., 2022, Time-lapse record of an earthquake in the dry felsic lower continental crust preserved in a pseudotachylyte-bearing fault: Journal of Geophysical Research: Solid Earth, v. 127, p. 1–32.

MS 6
Geoscience and construction materials, cultural heritage

Appointment

Session chairs

Description

Programme

MS 6Geoscience and construction materials, cultural heritage

Appointment

Session chairs

Description

Programme

MS 6
Geoscience and construction materials, cultural heritage