Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
10 results
Search Results
Item Open Access Fluid-phase transitions in a multiphasic model of CO2 sequestration into deep aquifers : a fully coupled analysis of transport phenomena and solid deformation(Stuttgart : Institut für Mechanik (Bauwesen), Lehrstuhl für Kontinuumsmechanik, Universität Stuttgart, 2017) Häberle, Kai; Ehlers, Wolfgang (Prof. Dr.-Ing. Dr. h. c.)Item Open Access Long-term lumped projections of groundwater balances in the face of limited data(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2024) Ejaz, Fahad; Nowak, Wolfgang (Prof. Dr.-Ing.)Item Open Access Stand und Entwicklungspotenziale der landwirtschaftlichen Biogasnutzung in Baden-Württemberg : ein regionalspezifischer Vergleich(Stuttgart : Universität Stuttgart, Institut für Energiewirtschaft und Rationelle Energieanwendung, 2017) Stenull, Maria; Voß, Alfred (Prof. Dr.-Ing.)Die Zielsetzung dieser Arbeit besteht darin, den Stand und die zukünftigen Entwicklungsmöglichkeiten für die landwirtschaftliche Biogasnutzung in Baden-Württemberg auf der Basis einer hohen regionalen Auflösung zu erheben und dabei zu analysieren, welche Unterschiede es in den Regionen gibt. Dabei werden „typische Modellanlagen“ für die Regionen Baden-Württembergs unter Berücksichtigung der bestehenden regionalen Agrarstruktur identifiziert und bewertet. Im Ergebnis werden Strategien für die Entwicklung der Biogasnutzung in Baden-Württemberg aus technologischer, ökonomischer und ökologischer Sicht vorgeschlagen. Hierfür wurden zuerst Biomassepotenziale zur Biogaserzeugung kleinräumig auf Landkreisebene ermittelt. Die Landkreise wurden in vier verschiedene Regionen (sog. Biogasregionen) zusammengefasst, die sich durch einheitliche Eigenschaften für die Biogasproduktion in Bezug auf Substratverfügbarkeit auszeichnen: die ackerreiche und gülledurchschnittliche Biogasregion 1 (BG1) im Nordwesten, die ackerland-, grünland- und güllereiche Biogasregion 2 (BG2) im Nord- und Südosten, die grünlandreiche und gülledurchschnittliche Biogasregion 3 (BG3) überwiegend im Südwesten und die ackerland- und grünlandarme Biogasregion 4 (BG4) in Mitte-Westen von Baden-Württemberg. In den so gebildeten Biogasregionen wurden anschließend die Analyse der Potenzialausnutzung und die Bilanz der Biogasnutzung dargestellt. Die Ergebnisse zeigen, dass bei der gegenwärtigen Substratzusammensetzung der Biogasanlagen nur die Energiepflanzenpotenziale im hohen Ausmaß ausgeschöpft werden. Die Anlagen, die überwiegend auf Basis von Energiepflanzen betrieben werden, könnten insgesamt bis zu 2,43 TWhel/a (Strategie „niedrige CO2-Vermeidungskosten“) Strom erzeugen (2020). Eine deutliche Steigerung der Stromerzeugung (auf 3,39 TWhel/a) kann nur erreicht werden, wenn im Schnitt Anlagen in der Größenklasse <100 kWel, mit hohen Gülleanteilen in der Substratzusammensetzung zugebaut werden (Strategie „Ausnutzung Biomassepotenzial“). Um die freien Gülle- und Dauergrünlandpotenziale maximal auszuschöpfen, müsste die Substratzusammensetzung der zukünftig zugebauten Biogasanlagen grundlegend geändert werden.Item Open Access Stochastic model comparison and refinement strategies for gas migration in the subsurface(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2023) Banerjee, Ishani; Nowak, Wolfgang (Prof. Dr.-Ing.)Gas migration in the subsurface, a multiphase flow in a porous-medium system, is a problem of environmental concern and is also relevant for subsurface gas storage in the context of the energy transition. It is essential to know and understand the flow paths of these gases in the subsurface for efficient monitoring, remediation or storage operations. On the one hand, laboratory gas-injection experiments help gain insights into the involved processes of these systems. On the other hand, numerical models help test the mechanisms observed and inferred from the experiments and then make useful predictions for real-world engineering applications. Both continuum and stochastic modelling techniques are used to simulate multiphase flow in porous media. In this thesis, I use a stochastic discrete growth model: the macroscopic Invasion Percolation (IP) model. IP models have the advantages of simplicity and computational inexpensiveness over complex continuum models. Local pore-scale changes dominantly affect the flow processes of gas flow in water-saturated porous media. IP models are especially favourable for these multi-scale systems because using continuum models to simulate them can be extremely computationally difficult. Despite offering a computationally inexpensive way to simulate multiphase flow in porous media, only very few studies have compared their IP model results to actual laboratory experimental image data. One reason might be the fact that IP models lack a notion of experimental time but only have an integer counter for simulation steps that imply a time order. The few existing experiments-to-model comparison studies have used perceptual similarity or spatial moments as comparison measures. On the one hand, perceptual comparison between the model and experimental images is tedious and non-objective. On the other hand, comparing spatial moments of the model and experimental images can lead to misleading results because of the loss of information from the data. In this thesis, an objective and quantitative comparison method is developed and tested that overcomes the limitations of these traditional approaches. The first step involves volume-based time-matching between real-time experimental data and IP-model outputs. This is followed by using the (Diffused) Jaccard coefficient to evaluate the quality of the fit. The fit between the images from the models and experiments can be checked across various scales by varying the extent of blurring in the images. Numerical model predictions for sparsely known systems (like the gas flow systems) suffer from high conceptual uncertainties. In literature, numerous versions of IP models, differing in their underlying hypotheses, have been used for simulating gas flow in porous media. Besides, the gas-injection experiments belong to continuous, transitional, or discontinuous gas flow regimes, depending on the gas flow rate and the porous medium's nature. Literature suggests that IP models are well suited for the discontinuous gas flow regime; other flow regimes have not been explored. Using the abovementioned method, in this thesis, four macroscopic IP model versions are compared against data from nine gas-injection experiments in transitional and continuous gas flow regimes. This model inter-comparison helps assess the potential of these models in these unexplored regimes and identify the sources of model conceptual uncertainties. Alternatively, with a focus on parameter uncertainty, Bayesian Model Selection is a standard statistical procedure for systematically and objectively comparing different model hypotheses by computing the Bayesian Model Evidence (BME) against test data. BME is the likelihood of a model producing the observed data, given the prior distribution of its parameters. Computing BME can be challenging: exact analytical solutions require strong assumptions; mathematical approximations (information criteria) are often strongly biased; assumption-free numerical methods (like Monte Carlo) are computationally impossible for large data sets. In this thesis, a BME-computation method is developed to use BME as a ranking criterion for such infeasible scenarios: The \emph{Method of Forced Probabilities} for extensive data sets and Markov-Chain models. In this method, the direction of evaluation is swapped: instead of comparing thousands of model runs on random model realizations with the observed data, the model is forced to reproduce the data in each time step, and the individual probabilities of the model following these exact transitions are recorded. This is a fast, accurate and exact method for calculating BME for IP models which exhibit the Markov chain property and for complete "atomic" data. The analysis results obtained using the methods and tools developed in this thesis help identify the strengths and weaknesses of the investigated IP model concepts. This further aids model development and refinement efforts for predicting gas migration in the subsurface. Also, the gained insights foster improved experimental methods. These tools and methods are not limited to gas flow systems in porous media but can be extended to any system involving raster outputs.Item Open Access Misfit-layered cobalt oxides for thermoelectric energy conversion(2017) Büttner, Gesine; Weidenkaff, Anke (Prof. Dr.)The conversion of waste heat into electrical current by a thermoelectric converter can significantly contribute to a more sustainable usage of our resources. The p-type misfit-layered [Ca2CoO3-δ][CoO2]1.62 is known for its promising conversion efficiency, which yet needs to be improved significantly for commercial applications. The efficiency of a material increases with the Figure of Merit ZT=σα^2/κ, with Seebeck coefficient α, electrical conductivity σ, and thermal conductivity κ. The aim of this thesis is to provide a better understanding of the electrical and the thermal properties of the complex [Ca2CoO3 δ][CoO2]1.62 and to use this understanding to improve the efficiency of converters. Accordingly, (i) the increase of ZT via cation substitution is shown; (ii) a better understanding of the electrical transport above room temperature is developed; (iii) the effect of stoichiometric defects and secondary phases on the thermoelectric properties is investigated. Finally, (iv) [Ca2CoO3 δ][CoO2]1.62 - CaMn0.97W0.03O3 δ - converters are fabricated and the efficiency is increased by a suitable converter design. More specifically, the unexplored influence of Ru and In substitution on the thermoelectric properties of the polycrystalline [Ca2CoO3 δ][CoO2]1.62 is investigated. While In does not have a positive effect, Ru for Co substitution increases ZT up to 20 %. This increase stems from a strong reduction of the thermal conductivity - which is probably induced by resonance scattering - while the decrease of the power factor α^2 σ is minor. The electrical transport mechanism of pure and Ru-substituted [Ca2CoO3 δ][CoO2]1.62 between room temperature and 800 K so far lacks a coherent theoretical model. Surprisingly, the framework of Anderson localization, which was developed to describe conduction in an impurity band of semiconductors, can be applied to the oxide. The Anderson model assumes that transport happens via charge-carrier hopping in a random Coulomb potential. For [Ca2CoO3 δ][CoO2]1.62, charges are considered to hop between Co sites in the CoO2 layer, while the random potential originates from interactions with the mismatched Ca2CoO3 δ layer. The presence of the ionized Ru atoms further alters the Coulomb potential, which increases the activation energy of the transport behavior. This understanding might contribute to the development of better theoretical models for the prediction of the thermoelectric properties of substituted [Ca2CoO3 δ][CoO2]1.62 compounds. A further improvement of the materials efficiency can be achieved by systematic introduction of stoichiometric defects and impurity phases. Here, the unexplored influence of the Co/Ca ratio on the thermoelectric properties of [Ca2 wCoO3 δ][CoO2]1.62, and the effect of Co3O4 impurity phase are investigated. It is shown that an increasing Co/Ca ratio in the [Ca2 wCoO3 δ][CoO2]1.62 phase leads to a larger figure of merit ZT induced by a strong resistivity drop. The decrease of resistivity stems from additional p-type charge carriers created by the formation of Ca vacancies. The Co3O4 impurity phase increases the thermal conductivity of the composite samples and leads to a reduction of ZT when the volume fraction of the Co3O4 phase is increased from 1% to 3%. Hence, the best figure of merit is expected close to the upper phase boundary of the [Ca2 wCoO3 δ][CoO2]1.62 phase. Not only the figures of merit of the materials, but also the design of a thermoelectric converter determines the device efficiency. In a converter, a p-type and a suitable n-type thermoelectric material are connected electrically in series and thermally in parallel. Here, [Ca2 wCoO3 δ][CoO2]1.62 is combined with the n-type CaMn0.97W0.03O3-δ and the device efficiency is improved by a variation of the ratio A_p/A_n of the cross section areas of the legs. The good agreement between the experimental values and the predictions of the compatibility model show the high quality of the fabricated devices and the value of the model for the optimization of the converter design. The adjustment of A_p/A_n improves the power output and the efficiency of the converters, where the best volume and area power densities exceed published high temperature values. The achieved efficiency of 1.08 % at a temperature of 1085 K at the hot side is close to the theoretical expected efficiency and can be further improved via ZT.Item Open Access Projektabschlussbericht zum "Teilvorhaben Korrosionsverhalten" (FKZ 0325497B (MPA) + FKZ 0325497A (DLR)) des Verbundvorhabens "MS-Store - Flüssigsalzspeicher-Testanlage und neue Fluide"(2018) Kaesche, Stefanie; Rückle, Dagmar; Bauer, Thomas; Bonk, AlexanderZiel des Teilvorhabens „Korrosionsverhalten“ im Verbundprojekt MS-Store - Flüssigsalzspeicher-Testanlage und neue Fluide war es, Anforderungen an die zu verwendenden Werkstoffe, die durch hohe Temperaturen bei Energiespeichern in solarthermischen Kraftwerken auftreten, hinsichtlich des Korrosionsverhaltens zu untersuchen, um die Lebensdauer solcher Kraftwerke zu erhöhen, sowie substantielle wissenschaftliche Ergebnisse in diesem Anwendungsgebiet zu erhalten. Mittels Auslagerungsversuchen bei 560°C wurden die Abtragsraten für verschiedene Stähle in unterschiedlichen Nitratsalzmischungen in Abhängigkeit von der Auslagerungsdauer isotherm und zyklisch bestimmt. Im Anschluss wurden mittels diverser elektronenmikroskopischer und röntgenografischer Untersuchungsmethoden (FIB, REM, EDX; TEM; XRD) die Oxidschichtentwicklung und -beschaffenheit, die Phasenzusammensetzung der Oxidschicht, die Gefügestruktur des Grundwerkstoffs, sowie der erfolgte korrosive Angriff analysiert. Mittels elektrochemischer Prüfmethoden (OCP, IE, EIS) wurde das Korrosionsverhalten der Stähle in-situ bei Temperaturen zwischen 410 und 560°C und in Abhängigkeit der Reinheit der Salzschmelze analysiert, sowie die Stabilität der Oxidschichten evaluiert. Es zeigte sich eine eindeutige Überlegenheit der Korrosionsbeständigkeit der untersuchten Cr,Ni-Stähle gegenüber des hochwarmfesten Cr-Stahls, speziell in Salzschmelzen die Chloridgehalte ab 0,5 Gew.-% aufweisen. Weiterhin ließ sich eine eindeutige Abhängigkeit des Korrosionsverhaltens von der gewählten Temperatur nachweisen; die Beständigkeit ist bei 410°C deutlich höher, als bei 560°C. Die mehrlagigen Oxidschichten bestehen aus Cr,Fe-Mischoxiden, sowie reinen Cr-/Fe-Oxiden. Sie weisen eine hohe Porosität, sowie eine schlechte Haftung auf dem Grundmaterial auf. Nach langer Auslagerung entstehen zusätzlich Na,Fe-reiche Oxide. Im Grundmaterial bildeten sich durch Stickstoffeintrag aus der Salzschmelze an den Korngrenzen oder auch im kompletten Gefüge Gefügeveränderungen, in Form von Cr-Nitriden. Neuartige elektrochemische Untersuchungen in Nitratsalzschmelzen bei hohen Temperaturen wurden mittels elektrochemischer Impedanzspektroskopie (EIS) durchgeführt. Dabei wurde die Abhängigkeit des Korrosionsverhaltens von Temperatur, Salzreinheit und Beschaffenheit und Stabilität der Oxidschichten ermittelt. EIS eignet sich sehr gut, um schnell fundierte Aussagen über ein vorliegendes Korrosionssystem zu treffen und kann auch in anderen Schmelzen, sowie anderen Werkstoffen oder Parametern eingesetzt werden. Die quantitative Auswertung dieser Messmethode ist sehr komplex und benötigt anwendungsbasierte Weiterentwicklung. Dennoch konnte das Auftreten des Breakaway-Effektes mittels dieser Methodik bestätigt werden. Außerdem wurde die Tendenz von Chrom zur Lösung in der Salzschmelze festgestellt, sowie Änderungen im Nitrat/Nitrit-Verhältnis, bedingt durch Zersetzungsreaktionen der Salzschmelze beobachtet. Diese Effekte können zu veränderten Eigenschaften der Schmelze hinsichtlich ihrer Wärmespeicherkapazität, ihrer generellen Stabilität und ihrer Korrosivität führen. Die im Verlauf des Teilvorhabens gewonnenen Erkenntnisse erweitern den bisher in der Fachliteratur präsentierten Kenntnisstand des Korrosionsverhaltens von anwendungsrelevanten Stählen in Nitratsalzschmelzen deutlich. Sie ermöglichen eine gezielte Materialauswahl für Planer und Konstrukteure von solarthermischen Kraftwerken.Item Open Access Nanomechanische und nanoelektrische rasterkraftmikroskopische Analyse von Polymerelektrolytbrennstoffzellen(2022) Morawietz, Tobias; Friedrich, K. Andreas (Prof. Dr. rer. nat.)Die vorliegende Arbeit beschäftigt sich mit der Analyse von Brennstoffzellenkomponenten. Dabei wird der Fokus dieser Arbeit auf die Analyse der katalytischen Schichten mit dem Rasterkraftmikroskop gelegt. Das Rasterkraftmikroskop kann Strukturen mit wenigen Nanometern auflösen und dabei die materialspezifischen Eigenschaften aufzeichnen. Der Einsatz und die Weiterentwicklung von Rasterkraftmikroskop basierten Messmethoden für diesen Anwendungszweck wird in dieser Arbeit dargelegt. Die (Nano)-Struktur von vielen Brennstoffzellenkomponenten konnte mit den bisherigen verwendeten Methoden nicht vollständig aufgeklärt werden. Vor allem die Struktur des Ionomers innerhalb der Elektrode ist eine Unbekannte. Über das materialsensitive Rasterkraftmikroskop kann die Identifikation und Strukturanalyse der einzelnen Komponenten der katalytischen Schichten erfolgen. Die Struktur und die mechanischen und elektrischen Eigenschaften des Ionomers in der Elektrode ist für den Massentransport und die ionische/elektronische Leitfähigkeit von Bedeutung. Um die Eigenschaften des Ionomers in den Elektroden zu beschreiben, wurde die Nanostruktur des Polymerelektrolyten auf verschiedenen Größenskalen untersucht. Es werden in dieser Arbeit ultra-dünne Schichten und deren Eigenschaften, sowie die Ausbildung von Grenzschichten zur Gasphase beschrieben. Ausgegangen wird von der Struktur einzelner Ionomerbündel welche auf verschiedene Substrate abgesetzt wurden. Die Struktur dieser Primärstrukturen und die Ausbildung erster Schichten werden für Ionomere mit unterschiedlichem Äquivalentgewicht beschrieben. Es wurden eine minimale Bündelhöhe von 1,5 nm und ein lamellarer Aufbau von den Schichten gemessen. Die Bündelhöhe wird in Abhängigkeit von Temperatur und relativen Luftfeuchte dargestellt. Ultra-dünne Ionomerschichten wurden als Model für Schichten in den Elektroden hergestellt. Als Ultra-dünne Schichten werden Schichten bezeichnet, welche eine Dicke kleiner als 100 nm besitzen. Sehr dünne Schichten (< 12 nm) zeigten in den Messungen keine oder nur sehr geringe ionische Leitfähigkeit durch die Schicht. Mit katalytisch aktiven AFM Spitzen wurde eine Querleitfähigkeit dieser sehr dünnen Schichten und eine Schichtdickenabhänigkeit der Ionenleitfähigkeit nachgewiesen. Dickere Schichten über einen Mikrometer wurden über ein Tauchziehverfahren erzeugt, um die Ausbildung der kristallinen Bereiche sowie der Grenzphase zur Gasphase von Membranen mit bekannter Vorgeschichte zu beschreiben. In den Messungen zeigten sich Bereiche mit erhöhter Steifigkeit. Die Messungen der Steifigkeit konnte eine Proportionalität zur mit Dynamische Differenzkalorimetrie gemessenen Kristallinität der Ionomere gezeigt werden. Die Kristallinität nahm mit zunehmendem Äquivalentgewicht und Alter der Schichten zu. Die Untersuchungen der katalytischen Schichten mit dem Rasterkraftmikroskop zeigten einen deutlichen Kontrast in den Materialeigenschaften der katalytischen Schichten zwischen dem Ionomer und dem Katalysator. Dabei kann die Struktur sehr hoch aufgelöst vermessen werden. Je nach verwendeter Spitze liegt die laterale Auflösung zwischen 1-25 nm. Das Ionomer konnte durch höhere Adhäsion und Deformation, eine niedrigere Steifigkeit sowie keinen elektronischen Strom identifiziert werden. An Messungen der Oberfläche wurden die Bereiche, die den Katalysator umhüllen, sowie größere zusammenhängende Ionomerbereiche gemessen. An Mikrotom-Querschnitten, wurden in den katalytischen Schichten Ionomerschichten in einer Größe gefunden, die auch durch die ultra-dünnen Schichten als Modellelektroden erzeugt werden konnten. Diese Ionomerschichten umhüllen die Katalysatorpartikel. Die Dicke der Schichten lag im Bereich von ~2,5 nm - 15 nm und war abhängig von der Temperatur und relativen Luftfeuchte. Außerdem scheint die Ionomerschichtdicke von dem Herstellungsverfahren abhängig zu sein. Nach Betrieb der Brennstoffzellen wurde eine Abnahme der Schichtdicke festgestellt. Ein Zusammenhang zwischen Ausgangsschichtdicke und irreversibler Degradationsrate durch den Brennstoffzellenbetrieb wurde gezeigt. Nach Betrieb wurde über Rasterelektronenmikroskop-Messungen unterstützend eine Abnahme der Elektroden- und Membrandicke gemessen. Eine Abnahme des Gesamtionomers konnte über das Rasterkraftmikroskop, Energiedispersive Röntgenspektroskopie und Infrarotspektroskopie gezeigt werden. In der Membran bildete sich nach Betrieb ein Platinband, welches von der Position der Probe in der Membran Elektroden Einheit abhängig war. Eine Korrelation zwischen Degradationsrate und Ablagerung von Platin in der Membran konnte gezeigt werden. Die Ablagerung kann in sehr großem Ausmaß stattfinden, dass Kurzschlüsse durch die Membran festgestellt werden konnten, welche mit dem Rasterkraftmikroskop nachgewiesen werden konnten. In der Bildanalyse Software GeoDict wurden Modelle von den Elektroden nach den gemessenen Daten erstellt und verschiedene Faktoren, wie Ionomerschichtdicke, Katalysatordurchmesser und Bedeckung des Katalysators mit Ionomer auf die resultierende ionische und elektronische Leitfähigkeit untersucht. Zusammenfassend trägt diese Arbeit zur Aufklärung der Struktur und Eigenschaften von Polymerelektrolytbrennstoffzellen bei und zeigt Degradationsmechanismen auf.Item Open Access Scale-up of gas fermentations : modelling tools for risk minimisation(2020) Siebler, FloraThe reduction of greenhouse gas emissions is a global endeavour supported by society, politics and industry. In recent years, circular economy, reducing the exploitation of fossil energy sources, have increased the demand for new solutions when producing commodities and fine chemicals. Caboxydotrophic fermentations with acetogenic bacteria are potential processes in order to reach these goals. They convert gaseous substrates such as CO, and CO2/H2 mixtures. However, gases as sole substrate are rather challenging, not only in small lab-scales but especially in large-scale. Transferring an efficient fermentation process from experimental to industrial scales often results in unpredictable performance losses. This study presents an in silico concept minimising possible risks in gas fermentations up-scaling. First, the economical feasibility of various fermentation methods is investigated. Then, two computational tools are presented using Clostridium ljungdahlii as model organism and synthesis gas as substrate in a 125 m3 bubble column reactor. The combination of economical investigation with modelling tools show high potential for successful scale-up of gas fermentations. With this concept feasibility, reactor design, operation mode and general risk minimisation can be analysed and specified.Item Open Access Zechstein Kupferschiefer at Spremberg and related sites : hot hydrothermal origin of the polymetallic Cu-Ag-Au deposit(2019) Spieth, Volker; Massonne, Hans-Joachim (Prof. Dr.)Copper-silver-gold-polymetallic (Cd, Hg, Mo, Co, Ni, Cr, V, Sb, U, Cs, Re, Pb, Zn, PGE) rich mineralization is present in the deposits containing Kupferschiefer black shale of the lowermost Zechstein Group of Late Permian (Lopingian) age in central Germany and southwestern Poland. Mineralized areas are near large shear lineaments at the border between the Saxo-Thuringian and Rheno-Hercynian zones. Polymetallic mineralization is contained in and geochemically transgresses the Upper Permian Rotliegend strata: the Weissliegend Sandstone, the Zechstein conglomerate, the Kupferschiefer sensu stricto, the Zechstein dolostone, and the overlying Werra carbonate rocks of the Zechstein Group. Hematitic alteration features of the Rote Fäule type are massively present. The mineralization occurs on a continental scale of more than 750 km in an east-westerly direction from eastern Poland to the Rhön near the Rhine valley in Germany in the so called European Copper Belt. The Spremberg-Graustein-Schleife Kupferschiefer deposit in the Lausitz of southeastern Germany has been newly explored and shows the high-grade metallic features of the typical Kupferschiefer deposits, e.g. in the Mansfeld area of Germany and the Lubin area of Poland. The deep drilling campaign from 2008 to 2010 produced much new sample material that became the basis for this scientific research undertaking, which is the first comprehensive study of its type in decades. The major focus of the study was to establish the nature and occurrence of the mineralization in its stratigraphic and ore depositional environment. The methodology employed was: (1) Geological mapping and sampling in the Spremberg-Graustein-Schleife deposit from the new drilling as well as from the drill repository of the LBGR Geological Survey of Brandenburg. This was also done in addition at the Rhön project, the Sangerhausen-Wettelrode deposit in Germany and the Konrad, Lubin, Polkowiecze-Sierosowiecze and Rudna deposits in Poland. (2) The SGS analytical services in Montreal, Canada, geochemically analyzed more than 800 rock powder samples of the exploration campaign 1956 to 1980 at Spremberg, as well as hundreds of new drill core assays were prepared from the new Spremberg exploration campaign. (3) Optical microscopy of more than 1,350 thin and polished rock sections were reviewed and the most important and significant ones were selected for detailed analysis. (4) Electron-microprobe (EMP) analytics, in which chemical compositions of minerals were determined. Textural relations were documented by back-scattered electron images. X-ray maps were produced to recognize the chemical zonation of minerals. 350 polished and thin sections from drill holes and underground locations were selected and analyzed. 626 measurements were taken of stoichiometric and non-stoichiometric metallic minerals, which resulted in new insights about their hot hydrothermal origin and depositional environment. Scanning electron microscope (SEM) studies with wavelength dispersive X-ray spectroscopy microprobe analyses (WDS) were conducted with the CAMECA SX 50. For the calculation of the mineral formulas and the mineral distribution diagrams, the Mincalc-5-program was used. (5) The Raman spectra were measured with the Horiba XpLora Raman microscope with confocal optics with laser wavelengths of 532 and 638 nm. The research focused on minerals and inclusions that were in the size fraction between 1 and 50 nm. Metallic minerals and hydrocarbon aggregates were identified and their intensity frequencies determined. (6) δ34S isotope analysis was conducted on 55 samples that were specifically selected to represent single sulfide aggregates to demonstrate the multi-phase nature of the mineralization. The mineral concentrates were analyzed with an EA-analyzer to SO2 at a reaction temperature of 1,050 °C. The S-isotopic composition was measured with a NC 2500 connected to a Thermo Quest Delta+XL mass spectrometer. The results confirmed the multi-phase nature of the deposit mineralization and supported the new model of origin. (7) Rock samples in historical and significant museum collections were reviewed and evaluated at the following places: Geological Collection at Universität Tübingen, Mansfeld Museum, Wettelrode Röhrigschacht Museum, German Federal Geological Survey Museum at Potsdam, Freiberg Bergakademie Mineralogical Museum, Polish Geological Museum, Warsaw, and Collection of the Mineralogical Institute of University Cracow, Poland. (8) Research progress was presented and discussed in-house and with national and international researchers at seminars, conferences and through publications. The new research results show that the high-grade, Upper Permian, Zechstein polymetallic deposits indicate strong chemical and paragenetic relationships that lead to a unified genetically linked model related to deep-sourced, hot hydrothermal, rift-related volcanism. Mantle heat during failed, intra-continental rifting of the Pangea supercontinent at the end of the Permian time released vast amounts of the exotic metal-rich, alkali-rich, silica-aluminum-rich, organic-rich, halogen-rich, high-density brines into deep-basement fractures, depositing them above the continental flysch Rotliegend sandstones and conglomerates. Detailed investigations show that the high-grade, exotic metal and hydrocarbon mineralization has a hot hydrothermal origin. These result in a micro-layered deposit that was extruded on the Upper Permian Rotliegend peneplain that may have been covered with a shallow Zechstein sea, which was very hostile to lifeforms, at the time of the Permian Mass Extinction. The mineral assemblies are unusual, often chemically non-stoichiometric and unique in their composition as they contain high-temperature and low-temperature minerals adjacent to each other. The stability fields of the sulfides indicate the temperature ranged between 72 °C and 557 °C and up to 1,120 °C for high digenite. Mineralogical results obtained through microscopy, microprobe, Raman spectroscopy, geochemistry and δ34S isotope analysis in this thesis show that: o The Kupferschiefer deposit type mineralization in its vast majority is somewhat monotonous, as it is made up in Spremberg and the European Copper Belt mainly of chalcocite (Cu2S), digenite (Cu1.75S5), covellite (CuS), bornite (Cu5FeS4), and chalcopyrite (CuFeS2), plus a high hydrocarbon content, which is significant as it occurs over a distance of more than 750 km in length. o Many of the copper minerals are of non-stoichiometric composition and unusual association. Bornite, chalcocite, chalcopyrite and pyrite occur as spherules, immiscible metallic drops in the slurry mud. Bornite of the Kupferschiefer sensu stricto T 1 layer often shows exsolutions of electrum (AuAg) and other solid state exsolutions with chalcopyrite and covellite, indicating pre-mixture in the rising metal-hydrocarbon mud slurry and rapid cooling after extrusion on the sea floor surface. o The microprobe element analysis of sulfide phases that are widespread in natural ores of the Kupferschiefer Cu-Ag deposits plot in a phase field that includes chalcocite, digenite, djurleiite, anilite, yarrowite (“blaubleibender” covellite), klockmannite, and krutaite. Klockmannite (CuSe) and krutaite (CuSe2) have a stability field of about 343 °C and 384 °C and thus document the high hydrothermal nature of the mineral deposition. o The δ34S sulfur stable isotopes are a unique feature to the Kupferschiefer sensu stricto and at Spremberg have a similar composition as those of the copper mineralization of the other deposits of the European Copper Belt. The δ34S sulfur stable isotopes are light to very light with values ranging from -31‰ to -40‰ (permille) in chalcocite-digenite and chalcopyrite samples of the lower Kupferschiefer sensu stricto. Given the high temperature of the sulfide mineralization, these low values cannot be explained by microbial reduction. As it is shown in published diagrams, deep-sourced systems of ultramafic to serpentinitic origin and composition can contribute brines with a similar δ34S sulfur stable isotope composition. o Geochemical major and trace element compositions are anomalous and are much enhanced compared to average global black shale. The Kupferschiefer sensu stricto analysis and geostatistical comparison diagrams demonstrate the interdependence of the base, precious and polymetallic mineralization with the hydrocarbon deposition in the Zechstein rocks. o Geometallurgical analysis of the available operational and scientific data proves the genetic association of the enriched ultrabasic-sourced elements PGE, Co, Ni, Cr, V, Se, Re, Os with the contemporaneously deposited hydrocarbons. o Geological observation and mineralogical analyses demonstrate that the hematitic “Rote Fäule” is a post Zechstein Kupferschiefer, pervasive alteration event. In places, the “Rote Fäule” may have two distinct phases, of which one might have added gold to the system, forming independent new deposits. The advancing “Rote Fäule” front creates a “TZ Transition Zone”, where existing base and precious metals are enriched to a higher grade. o The age of the Zechstein Kupferschiefer deposition is considered to be 252.5 M.y. This might vary slightly along the 750 km of the European Copper Belt. The age dating relies on illite and rhenium-osmium ages. Spremberg samples have been submitted to age dating. The mineralization has a multi-phase history with age dates spreading from 267.7 M.y. to the “Rote Fäule” alteration event date of 244.5 M.y. o Large, deep-reaching, continent-size rifting lineaments are known in the Zechstein mineralized area of the European Copper Belt. These NW-SE lineaments are disrupted by NE-SW faults. This tectonic pattern is common in all Kupferschiefer districts and has been demonstrated with a seismic exploration program at Spremberg. Geological observations and mapping in Sangerhausen-Wettelrode, Spremberg and the Lubin-Rudna district show that: o The Weissliegend sand is an injectite/extrudite, silica slurry of Zechstein age that mostly rests on top of the Permian Rotliegend peneplain and is covered in an undulating manner by Kupferschiefer sensu stricto. o The Weissliegend sands are cut by veins and veinlets of sulfides and hydrocarbon and Kupferschiefer-like black mud rock that may represent the feeder veins of an open, hot hydrothermal vent. o The Weissliegend sand hosts by far the majority in quality and quantity of the Kupferschiefer-type deposit mineable copper resources measured in 100s of million of tons. o These observations resulting in a high-temperature, hydrothermal emplacement model lead in their conclusion to a paradigm change that replaces the “obsolete” syn-sedimentary epigenetic model, with consequences: - future exploration and mine development, - can rely on parameters that are congruent with the scientific knowledge that in many aspects resembles Volcanic Submarine Massive Sulfide deposits, and - will assist in the finding and development of the so far termed(by the USGS) “undiscovered Kupferschiefer resources”. • The new model for the Zechstein Kupferschiefer deposits postulates a high-energy, hot-hydrothermal, extrusive environment not dissimilar to submarine “Black Smoker” and volcanogenic, submarine, metal-brine deposits. The metal-rich fluids ascended through deep-reaching faults and erupted as slurries in low-relief, mud volcanism above fractures in an open, shallow, inland sea. Metal sulfide deposition is systematically accompanied by the precipitation of silica, dolomitic carbonate, and illite, as well as primary copper chlorides, such as atacamite (CuCl2) and other brine minerals, such as anhydrite and sylvite. • The ultimate brine source is interpreted to be serpentinized peridotite in the lower crust near the Moho transition to the mantle. Dehydration of the serpentinite source to talc (steatization) by mantle heat during failed, intra-continental rifting of the Pangaea supercontinent at the end of Permian time released vast amounts of element-laden, high-density brines into deep basement fractures, depositing them above the continental flysch sediment Rotliegend sandstone and conglomerate peneplain in the shallow Kupferschiefer sea, which is analogous to the modern northern Caspian Sea and the Salton Sea of southern California, USA.Item Open Access Behavior of concrete structures subjected to static and dynamic loading after fire exposure(2021) Lacković, Luka; Ožbolt, Joško (Prof. Dr.-Ing. habil.)The resistance of concrete structures exposed to extreme loading conditions such as explosion, impact, industrial accidents, tsunami, earthquake or their combination represents one of the major topics in research today. Such loading conditions are characterized with high loading rates often acting in conjunction with fire exposure. Especially vulnerable are the structures located in the seismically active areas with high level of urbanization and proximity to HAZMAT landfills, which additionally exacerbate fire conflagrations. The behavior of concrete changes significantly when exposed to elevated temperatures resulting in the decrease of its mechanical properties. Reinforced concrete (RC), when exposed to high temperature culminates in a simultaneous thermal behavior of its two constituents, steel and concrete, that should be considered in the analysis. It is also known that the resistance, crack pattern and failure mode in concrete are strongly influenced by the loading rate. The dynamic response of RC structures previously exposed to fire changes significantly when compared to initially undamaged RC structures. The main objective of the present work is to further improve the existing rate sensitive thermo-mechanical model for concrete through the following: (i) the implementation of the experimentally obtained thermal dependence of concrete fracture energy in the thermo-mechanical model, (ii) the calculation of concrete thermally dependent mechanical properties by means of nonlocal (average) temperature and (iii) to perform parametric study on fastening elements and RC frames in order to investigate the interaction between the thermally induced damage and mechanical behavior of structures. The experimental investigations in the present work indicated that the concrete fracture energy has a declining tendency with the temperature increase, measured on small and mid-sized concrete beams. This is implemented in the thermo-mechanical model and it is indicated that the decrease of fracture energy has a relatively mild influence on reaction values in terms of loading rate. However, its effect on the fracture patterns and reaction-time histories can be considered as more significant. The influence of the nonlocal temperature is validated against the experimental results carried out on RC frames which had been thermally pre-damaged and subsequently loaded with impact. Currently there are almost no models that can realistically predict the structural behavior at this level of complexity. Furthermore, a parametric study is carried out to show the influence of preloading of single-headed stud anchor and anchor group with two and four studs, on the residual concrete edge failure capacity after fire exposure. The anchors are exposed to fire and loaded in shear, perpendicular to the free edge of the concrete member up to failure, in both hot and cold state (after cooling). The influence of different geometry configurations and initial conditions such as the edge distance, embedment depth, anchor diameter and duration of fire on the load-bearing behavior of anchors is investigated. It is demonstrated that the preloading has a strong negative influence on the residual load-bearing capacity of the concrete. Finally, the numerical parametric study is performed to investigate the influence of fire duration and the loading rate on the resistance of RC frames. The response of the RC structures strongly depends on whether it was loaded in hot or residual (cold) state, i.e. after being naturally cooled down to ambient temperature. Furthermore, an extensive numerical investigation on the influence of post-earthquake fire on the residual capacity of RC frames with and without ductile detailing is conducted. The numerical investigation encompassed the validation of the thermo-mechanical model in terms of temperature distributions, thermal deflections and load-bearing capacity against the test data and subsequent parametric analysis with different levels of fire exposure ranging from 15 to 120 min.