An investigation into accelerated leaching for the purpose of ARD mitigation

World-wide, acid rock drainage (ARD) is one of the biggest environmental challenges facing environments with current or previously active mining activities. Formed from the exposure of sulphide mineral to both water and air, and catalyzed by naturally occurring iron- and sulphur-oxidizing micro-organisms, ARD pollution is predominantly associated with the mining of sulphidic ores and coal. Of particular concern are the large volumes of mining wastes from which the generation of ARD and the associated pollution effects often persist over tens to hundreds of years after mining operations have ceased. Current ARD management strategies focus on the prevention of ARD through mineral waste deposition or remediation options once ARD has formed. These strategies, however, do not remove the risk of ARD generation in the future. The aim of this study was to investigate the removal of the potential for ARD generation from a low-grade copper waste rock through the accelerated removal of the sulphur components via reaction. The three waste rock samples used in this investigation had total sulphur grades of between 2.20 and 3.20 % with the majority of the sulphide present as pyrite, chalcopyrite and galena. Significant quantities of non-sulphide associated iron minerals, predominantly magnetite, were also present in the three samples. The waste rock samples were sourced from mining operations in Chile and South Africa and had a D80 of approximately 0.8 cm. All three waste rock samples were potentially ARD generating

Application of the residue number system to the matrix multiplication problem

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references.Not availabl

Dislocation‐tuned electrical conductivity in solid electrolytes (9YSZ): A micro‐mechanical approach

Tailoring the electrical conductivity of functional ceramics by introducing dislocations is a comparatively recent research focus, and its merits were demonstrated through mechanical means. Especially bulk deformation at high temperatures is suggested to be a promising method to introduce a high dislocation density. So far, however, controlling dislocation generation and their annihilation remains difficult. Although deforming ceramics generate dislocations on multiple length scales, dislocation annihilation at the same time appears to be the bottleneck to use the full potential of dislocations‐tailoring the electrical conductivity. Here, we demonstrate the control over these aspects using a micromechanical approach on yttria‐stabilized zirconia ‐ YSZ. Targeted indentation well below the dislocation annihilation temperature resulted in extremely dense dislocation networks, visualized by chemical etching and electron channeling contrast imaging. Microcontact‐impedance measurements helped evaluate the electrical response of operating individual slip systems. A significant conductivity enhancement is revealed in dislocation‐rich regions compared to pristine ones in fully stabilized YSZ. This enhancement is mainly attributed to oxygen ionic conductivity. Thus, the possibility of increasing the conductivity is illustrated and provides a prospect to transfer the merits of dislocation‐tuned electrical conductivity to solid oxygen electrolytes

Roadmap on exsolution for energy applications

Over the last decade, exsolution has emerged as a powerful new method for decorating oxide supports with uniformly dispersed nanoparticles for energy and catalytic applications. Due to their exceptional anchorage, resilience to various degradation mechanisms, as well as numerous ways in which they can be produced, transformed and applied, exsolved nanoparticles have set new standards for nanoparticles in terms of activity, durability and functionality. In conjunction with multifunctional supports such as perovskite oxides, exsolution becomes a powerful platform for the design of advanced energy materials. In the following sections, we review the current status of the exsolution approach, seeking to facilitate transfer of ideas between different fields of application. We also explore future directions of research, particularly noting the multi-scale development required to take the concept forward, from fundamentals through operando studies to pilot scale demonstrations

Oxygen exchange pathways of platinum model electrodes on yttria-stabilized zirconia

Die elektrochemische Sauerstoff-Austauschreaktion an Platinelektroden auf Yttrium-stabilisiertem Zirconiumdioxid (YSZ) ist sowohl eine hochinteressante Mo-dellreaktion für grundlegende Untersuchungen der Elektrodenkinetik an Festkörperi-onenleitern, als auch von großem technologischen Interesse, da sie in einer Vielzahl an elektrochemischen System eine entscheidende Rolle spielt (z.B in Lambda-Sonden, Hochtemperatur-Brennstoffzellen, Hochtemperatur-Elektrolysezellen oder bei der elektrochemischen Modifikation der katalytischen Aktivität von Katalysator Oberflä-chen).In der vorliegenden Arbeit wurde die Kinetik der Sauerstoff-Austauschreaktion mit Hilfe von geometrisch wohldefinierten, dichten Pt (111) Mikroelektroden auf YSZ (100) Einkristallen untersucht.Die Elektroden wurden durch Abscheidung dünner Pt Filme mittels Kathodenzerstäubung ("sputtern") auf dem YSZ Elektrolyt und nachfolgender Mikrostrukturierung mittels Fotolithographie hergestellt.Die elektrochemische Charakterisierung erfolgte mittels Impedanzspektroskopie, Strom-Spannungs Messungen und spannungsunterstütztem 18O-Tracer-Einbau in Kombination mit Flugzeit-Sekundärionen-Massenspektrometrie (time of flight secondary ion mass spectrometry, ToF-SIMS).Anhand von Impedanzmessungen bei hohen Temperaturen (550 - 900 °C) an Mikroelektroden unterschiedlicher Größe konnte auf einen Reaktionsmechanismus über einen Pt Oberflächenpfad mit einem ratenbestimmenden Schritt an der Dreiphasengrenze geschlossen werden.Bei niedrigeren Temperaturen (Als ratenbestimmender Schritt des Volumenpfads wurde Diffusion einer Sauerstoffspezies entlang der Pt Korngrenzen diskutiert.Mit Hilfe von 18O-Einbau in Kombination mit ToF-SIMS war es möglich die elektrochemisch aktive Zone (d.h. der Bereich, in dem Sauerstoff in YSZ eingebaut wird) abzubilden. Bei ~320 °C war die Einbauzone rahmenförmig und ihre Position und laterale Ausbreitung war von der Polarisation der Elektrode abhängig. Bei moderaten Überspannungen wurde Sauerstoff ausschließlich unter der Pt Elektrode eingebaut, bei hoher Polarisation hingegen breitete sich die Einbauzone auch auf die freie YSZ Oberfläche aus. Darüber hinaus ließen diese Experimente einen flächenbezogenen Pfad parallel zum Oberflächenpfad vermuten. Dieser flächenbezogene Pfad wird als jener Volumenpfad angesehen, der auch in elektrochemischen Impedanzmessungen identifiziert wurde.Mittels Gleichstrommessungen bei Temperaturen zwischen 600 und 720 °C wurde das Strom-Spannungs-Verhalten der Pt Modellelektroden im Oberflächenpfad-Regime untersucht und der dreiphasenbezogene Polarisationswiderstand bei Gleichgewichtsbedingungen konnte als Diffusionsprozess identifiziert werden. Ein möglicher Elementarprozess, der dieses Verhalten erklären könnte, wäre Diffusion von Sauerstoff durch eine Verunreinigungsphase an der Dreiphasengrenze. Bei sehr hohen kathodischen Überspannungen wurde ein weiterer Reaktionspfad parallel zum diffusionslimi-tierten Dreiphasenpfad beobachtet. Dessen Reaktionsrate war exponentiell von der Überspannung abhängig und als wahrscheinlichste Interpretation dieses Verhaltens wurde Stöchiometrie-Polarisation des Elektrolyten diskutiert. In diesem Falle läuft die Sauerstoffreduktion auf der YSZ-Oberfläche ab, wobei die Elektronenversorgung über den Elektrolyten ratenbestimmend ist. Darüber hinaus handelt es sich beim dreiphasenbezogenen Prozess, der in den Tracer-Experimenten abgebildet wurde, höchstwahrscheinlich ebenfalls um diesen Reaktionspfad.Insgesamt kann somit gesagt werden, dass diese Arbeit einen substantiellen und neuen Beitrag zum tieferen Verständnis von Reaktionspfaden und Reaktionsmechanismen des Sauerstoffaustausches an Pt14

Die Kinetik der [O tief 2]-Reduktion an mikrostrukturierten Platinschichten auf Yttrium-stabilisiertem [ZrO tief 2]

Zsfassung in engl. SpracheBeim Betrieb von Hochtemperaturbrennstoffzellen kommt es durch Überspannungen zu erheblichen Verlusten, wobei die relativ schlechte Kinetik der elektrochemischen [O tief 2]-Reduktion als eine der Hauptursachen angesehen wird. Eine Klärung des entsprechenden Reaktionsmechanismus ist daher von großer Bedeutung. Poröse Elektroden - wie sie auch in realen Systemen eingesetzt werden - sind hierfür nur bedingt geeignet, da sie keine definierte Geometrie aufweisen.Mikrostrukturierte Dünnschichtelektroden dagegen ermöglichen vielfältige Aussagen zur Elektrodenkinetik.In dieser Arbeit werden Experimente zur [O tief 2]-Reduktionskinetik an Pt-Modellelektroden vorgestellt. Die Präparation von dichten Platinschichten auf Y-stabilisiertem [ZrO tief 2] (YSZ) erfolgte durch Magnetronsputtern auf 700°C heißes Substrat. Aus diesen Schichten wurden mittels Fotolithografie wohldefinerte Mikroelektroden mit verschiedener Form und Größe hergestellt und impedanzspektroskopisch im Temperaturbereich von 700 bis 900°C charakterisiert.Durch die Variation der Elektrodengeometrie konnte die Dreiphasengrenze - d.h. der Bereich Gasphase/Elektrode/YSZ - als der Ort des ratenbestimmenden Schrittes identifiziert werden. Messungen bei unterschiedlichen Temperaturen ermöglichten die Ermittlung der Aktivierungsenergie von 1.40eV dieses kinetisch langsamsten Teilprozesses.The actual performance of solid oxide fuel cells (SOFCs) is still unsatisfactory due to the high polarisation caused by relatively slow [O tief 2]-reduction kinetics. A clarification of the corresponding reaction-mechanism therefore stands in worldwide interest. Porous electrodes - as they are used in common SOFCs - suffer from the disadvantage of an ill-defined geometry. Microstructured thin-film-electrodes in contrast offer the possibility of manifold information in terms of electrode kinetics.In this work experiments on the [O tief 2]-reduction reaction on Pt-modelelectrodes will be presented. The preparation of dense platinum-films on yttria-stabilised zirconia (YSZ) was carried out by magnetron sputtering on 700°C hot substrate. From these layers well-defined microelectrodes of different shape and size were made by photolithography, which were characterised by impedance spectroscopy in a temperature range of 700 to 900°C.Through variation of the geometry of the microelectrodes the triple-phase-boundary (TPB) - i.e. the area gaseous phase/electrode/YSZ - could be identified as the site of the rate determining step.Measurements at different temperatures enabled the evaluation of 1.40eV being the activation energy of this kinetically slow-going step.14

Model composite microelectrodes as a pathfinder for fully oxidic SOFC anodes

All-oxide model-composite electrodes were established consisting of a thin, micropatterned, electronically conducting oxide, which acts as a current collector, and a thin film of gadolinia-doped ceria, which is an electrochemically highly active mixed conductor under reducing atmospheres. The choice of the current collecting oxides was based on their electronic conductivity assessed by measurements of thin films using the van der Pauw method. Lanthanum and niobium doped strontium titanate as well as alumina doped zinc oxide, were investigated this way in a humid hydrogen atmosphere. Promising materials were incorporated as a current collector into model-composite microelectrodes and tested for their stability and efficiency in electrochemically activating the microelectrode. Alumina doped zinc oxide, while being an excellent electron conductor, showed severe stability problems at temperatures above 600 °C. However, a microelectrode with a current collector of niobium doped strontium titanate (Sr0·9Ti0.8Nb0·2O3) performed comparable to an electrode with a Pt current collector and, additionally, showed an improved tolerance to sulphur poisoning in a humid hydrogen atmosphere with 10 ppm of hydrogen sulphide

Revisiting the Temperature Dependent Ionic Conductivity of Yttria Stabilized Zirconia (YSZ)

The temperature dependent conductivity of yttria stabilized zirconia (YSZ) exhibits a bending in Arrhenius’ plots which is frequently discussed in terms of free and associated oxygen vacancies. However, the very high doping concentration in YSZ leads to such a strong defect interaction that the concept of free vacancies becomes highly questionable. Therefore, the temperature dependent conductivity of YSZ is reconsidered. The conductivity of YSZ with different doping concentration was measured in a broad temperature range. The data are analyzed in terms of two different barrier heights that have to be passed along an average path of an oxygen vacancy in YSZ (two barrier model). For 8–10 mol% yttria, the two barriers are in the range of 0.6 eV and 1.1–1.2 eV, respectively. The conductivity and thus the barrier heights also depend on the cooling rate after a high temperature pre-treatment. This indicates that different frozen-in distributions of dopants affect the vacancy motion by different energy landscapes. Temporarily existing defect configurations, possibly with a strong effect of repulsive oxygen vacancy interaction, are suggested as the reason of high barriers. Future dynamic ab-initio calculations may reveal whether this modified model of the YSZ conductivity is mechanistically meaningful.Fonds zur Förderung der Wissenschaftlichen Forschun

Challenges of processing and operating metal supported fuel cells

Metal supported fuel cells (MSCs) are attractive for non-stationary energy applications like fuel cellgenerators or range extender for battery electric vehicles. Contrary to conventional anode (ASC) or electrolytesupported (ESC) solid oxide fuel cells, MSCs promise improved mechanical stability and less production costs. Asclose cooperation between Forschungszentrum Jülich, TU Wien, Plansee SE and AVL List GmbH, the ChristianDoppler Laboratory for Interfaces in Metal-supported Electrochemical Energy Converters contributes to thedevelopment of the Plansee MSC concept. A specific focus lies on the optimized processing of the electrodes aimingon increased electrochemical performance and long-term stability. Recently, significant progress in cell performancewas achieved by optimizing the sintering procedure of the cathode, enabling to introduce LSC as cathode material ofthe Plansee MSC. An adapted sintering route using an atmosphere with controlled oxygen partial pressure, optimizedparticle size and sintering aids enabled to improve the sintering behaviour of the cathode in moderate temperatures. Inparallel, Ni/GDC anode with optimized microstructure was introduced. Both measures resulted in a significant increaseof electrochemical performance. The presentation summarizes the latest results including a general discussion offactors which must be considered to achieve improved long-term stability as well