Scientific Events

The mechanisms of nucleation, growth and coalescence of voids leading to the fracture of ductile metals have been investigated for more than 50 years and modelled with increasing degrees of complexity. Nevertheless, we are still far today from a fully predictive approach, in particular in the context of the new generations of metallic alloys with advanced microstructures. Challenges remain on several fronts, for instance: the description of the statistical aspects of void nucleation, the transition into shear dominated failure mode, the physical meaning of the internal lengths entering non local models, the treatment of competing fracture mechanisms (e.g. intergranular versus ductile), etc. In this talk, recent progress made regarding the characterization and modelling of ductile fracture in Al alloys and in steel will be presented, insisting on void nucleation aspects. Topic: 9th MMELO Lecture - Prof. Thomas Pardoen Time: Febr 17, 2022 15:00h CET [more]

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In-situ transmission electron microscopy (TEM) allows researchers to analyse at the nano-scale and in ‘real time’ the electrochemical processes of the electrode materials within batteries during device operation. The active interface regions of such electrodes form solid electrolyte interface (SEI) layers during the charge and discharge cycling. The formation and movement of this functional SEI nano-interface is one of the main research fields in battery science, as it directly affects battery performance and lifetime. Of particular interest is observing the structural and chemical evolution of this lithium-rich, extremely complex polycrystalline interface. Si nanowires are attractive materials for applications such as lithium battery anodes due to their high theoretical capacity and ultra-low-cost for material sourcing and fabrication. The use of electrochemically active metals such as Sn for the growth of Si nanowires contributes to the overall specific capacity of the electrode. This study explores the phase change in both the Si nanowire metal seed head and the nanowire SEI layer during battery cycling. Our goal is to investigate the effect a chosen seed metal has on the Si electrode. We show that the lithiation/delithiation behaviour of the Sn-Si nanowire obtained using liquid cell was comparable to the result from bulk half-cell cycles and ex-situ analysis. Finally, we compare the benefits and drawbacks of liquid cell in-situ electrochemistry to cryogenic TEM analysis of the same system. Although in-situ electrochemistry TEM offers many advantages over other characterisation techniques, this analysis method is still in its infancy. [more]

In order to address climate change, we must transition to a low-carbon economy. Many clean primary energy sources, such as solar panels and wind turbines, are being deployed and promise an abundant supply of clean electricity in the near future. The key question becomes how to store, transport and trade this clean energy in a manner that is as convenient as fossil fuels. The Alternative Fuels Laboratory (AFL) at McGill University is actively researching the use of recyclable metal fuels as a key enabling technology for a low-carbon society. Metal fuels, reduced using clean primary energy, have the highest energy density of any chemical fuel and are stable solids, simplifying trade and transport. The chemical energy stored in the metal fuels can be converted to useful thermal or motive power through two main routes: the Dry Cycle, where metal powders/sprays are burned with air, or the Wet Cycle, where metal powders are reacted with water to produce hydrogen and heat as an intermediate step before using the hydrogen as a fuel for various power systems. This talk will overview the concept of metal fuels and the various power system options. It will also touch on the combustion and reaction physics of metal fuels and the propagation of metal flames. [more]

Electrochemical energy storage is the key enabling component of electric vehicles and solar/wind-based energy technologies. The enhancement of energy stored requires the detailed understanding of ionic transport and electrochemical and electromechanical phenomena on local scales which are not always accessible with classical electrochemical techniques, such as voltammetry. Therefore, local probing of electrochemical and electromechanical behaviors on individual structural elements and heterogeneities, from grains to defects and further to individual atomic and molecular species, are invaluable. In this talk, I want to introduce force-based atomic force microscopies (AFM) to provided novel insights into local electrochemical processes on tens of nanometer and even molecular length under electrochemical control. I will highlight the development and application of in situ/operando force-based AFM methods to gain insight into the local charge storage mechanism in a variety of energy related materials. In the first part of the talk, I will showcase how AFM can be used to investigate the structure and dynamics of the electric double layer (EDL) for electrochemical capacitors. I want to highlight work on room temperature ionic liquids on model graphene electrodes since ionic liquids hold the promise of increasing the electrochemical stability windows for electrochemical capacitors. AFM was used to observe topological defects and show the existence of structural domains parallel to the solid-liquid interface towards a full picture of the double layer structure and their change with applied bias. In the second part of the talk, I want to highlight how AFM-based methods can be used to study ionic transport and local electrochemical reactions in supercapacitors and battery materials. Here, electro-chemo-mechanical coupling is the key to study ion insertion pathways and heterogeneities in local redox reactions. The first is demonstrated for the cation insertion into layered Ti3C2 electrodes based on their change in mechanical stiffness whereas the second is highlighted for proton insertion into WO3 where the relationship between electrochemical current and electrode strain are discussed. [more]

The advent of solid-state batteries has spawned a recent increase in interest in lithium conducting solid electrolytes. However, many open questions remain when trying to optimize electrolytes and understand solid state battery chemistries. In this presentation, we will show how an understanding of the structure-transport properties can help tailor the ionic conductivity. In an exemplary study on superionic lithium metal halides, we show that a cation site-disorder and the local structure of materials is important to study, especially as synthetic influences control materials properties. In a second part of this presentation, we will show the tremendous influence of lattice dynamics on ionic conductors. By introducing a different approach to understanding ionic motion using phonon occupations, we try to explain so far unexplained behaviors of physical ionic transport. Finally, we will show that it is not only important to find fast ionic conductors, but that fast ionic conduction is paramount within solid state battery composites. Measuring the effective ionic transport in cathode composites provides an avenue to explore transport and stability limitations that in turn provide better criteria for solid state battery performance Bio: Wolfgang Zeier received his doctorate in Inorganic Chemistry in 2013 from the University of Mainz. After postdoctoral stays at the University of Southern California, the California Institute of Technology, and Northwestern University, he was appointed group leader at the University of Giessen, within the framework of an Emmy-Noether research group. Since 2020 he holds a professorship for Inorganic Chemistry at the University of Münster. In addition, he heads a department at the Helmholtz-Institute Münster, Ionics in Energy Storage. His research interests encompass the fundamental structure-to-property relationships in solids, with a focus on thermoelectric and ion-conducting materials, as well as solid-solid interfacial chemistry for all-solid-state batteries. [more]

The NanoSIMS is emerging as a powerful tool to study complex problems in materials science. The NanoSIMS is a high-resolution secondary ion mass spectrometry instrument capable of chemical mapping at 100 nm spatial resolution, detection limits in the ppm range and is able to detect almost all elements in the periodic table as well as isotopes. In this seminar I will show how we have been using the NanoSIMS to image localised deuterium in electrochemically charged steel and nickel alloys as well as in zirconium alloys oxidised in an autoclave to simulate nuclear reactor conditions. I will explain how isotopic tracers, such as 18O and deuterium, can be used to avoid imaging artefacts and provide temporal information. Some of the complexities associated with detecting hydrogen and deuterium in the NanoSIMS will be discussed. [more]