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Yasmin Ahmed Salem, M.A.
Yasmin Ahmed Salem
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Phone: +49 211 6792 722
Room: 222

Scientific Events

Scientific Events

Month:

13544 1523015705

In Situ Investigation of the Dynamic Evolution of Materials and Interfaces in Energy Storage Systems

Abstract: In energy storage devices, materials evolve from their initial state due to electrochemical reactions and interfacial instabilities at interfaces. To develop batteries with improved safety, energy density, and lifetime, it is critical to understand transformation mechanisms and degradation processes within these devices. In my research group, multiscale in situ techniques are used to reveal reaction mechanisms and interfacial transformations to guide the development of better batteries and other devices. Our recent work has used in situ transmission electron microscopy (TEM) to reveal phase transformation pathways and mechanical degradation/fracture when sulfide nanocrystals react with different alkali ions (lithium, sodium, and potassium). Surprisingly, mechanical fracture was found to occur only during reaction with lithium, despite larger volume changes during reaction with sodium and potassium. Since fracture is a known capacity decay mechanism in batteries, this result indicates that these materials are useful for the development of novel, high-energy sodium and potassium batteries. In a different study, operando synchrotron X-ray diffraction methods were used to precisely measure crystallographic strain evolution in battery electrode materials; this technique enables measurements beyond what is possible with TEM. In the final portion of the presentation, in situ X-ray photoelectron spectroscopy (XPS) experiments that reveal chemical evolution of solid-state interfaces in energy storage and electronic materials will be presented. Overall, this research demonstrates how fundamental understanding of dynamic processes can be used to guide the design and engineering of new materials and devices with high energy density and long lifetime. [more]

MPIE Colloquium

13560 1523516249

High Temperature Materials - Recent Developments for Future Challenges

The introduction of the talk provides an overview on materials research in IEK-2 (Institute for Energy and Climate Research, Materials Characterization) in Forschungszentrum Jülich. Selected examples of metallic and ceramic high performance materials for applications in energy conversion and storage systems are introduced, e.g. new materials for membranes, coatings or turbine blades. The main part of the presentation focuses on recent developments of novel high temperature Mo‑Si‑B materials, which are potential candidates to substitute Ni-base superalloys in power plants or aircraft turbines. Such alloys include a Mo solid solution phase as well as silicides, which are creep and oxidation resistant, but very brittle phases. The challenge is to balance the properties at ambient temperatures and high temperatures to tailor these multi-phase alloys for the use in a wide temperature range up to 1200°C and various mechanical loads. Concepts of material design, i.e. alloying strategy and process-microstructure-properties relationships are presented in terms of improved mechanical properties and oxidation resistance. The effect of additional elements on the mechanical properties, like fracture toughness, ductile-brittle-transition and creep resistance will be described. The presentation also includes the formation of isotropic and anisotropic microstructures by powder metallurgy, directional solidification and additive manufacturing. The latter process is quite challenging due to ultra-high melting temperatures of >2000°C and corresponding difficulties during melting and rapid cooling. [more]

Topic day “Novel materials and alloy design - microstructure property relationship” at the Metallkundekolloquium/Arlbergkolloquium

17690 1550059361

Topic day “Novel materials and alloy design - microstructure property relationship” at the Metallkundekolloquium/Arlbergkolloquium

“Experimental Nanomechanics” at the “16th European Mechanics of Materials Conference”

17676 1550059382

“Experimental Nanomechanics” at the “16th European Mechanics of Materials Conference”

Topical session “Mechanical Properties at Small Scales” at the DPG-Spring Meeting 2018

17675 1550059401

Topical session “Mechanical Properties at Small Scales” at the DPG-Spring Meeting 2018

MPIE Colloquium

12953 1519312993

Nanoindentation for Investigating Dynamics of Shear Bands in Metallic Glasses

Deformation in metallic glasses occurs by initiation and propagation of multiple thin shear bands. This mode is rather difficult to analyse since generally, a single band soon propagates to a large extent in the specimen leading to a catastrophic failure. Exceptions are for example in creep tests under very low stress and moderate temperature or in confined deformation tests. We used instrumented nano-indentations to perform series of independent experiments at room temperature on a Mg65Cu12.5Ni12.5(Ce75La25)10 metallic glass. Loading part of the curves shows serrations which size and duration were measured using an automatic procedure. To make analyses consistent, data were considered only in the domain with similar strain rates, in the range of 1 to 0.3 s-1. Times between successive serrations follow a normal distribution characterizing a random occurrence of deformation burst in the glass. It was then conjectured, first that serration occurs through activation of appropriate zone in the glass that should naturally scale with a multiple of an elementary domain size characterizing the deformation mechanism. Second, as activated zones leading to serration are very few in the glass, the model should be described by the Poisson statistics. Data analyses reveals that serration size are well fitted by a Poisson distribution. The model predict an elementary size which scale with that of the activation volume of 3 atoms, measured from creep test at constant load in the same series of experiments. Eventually, energy dissipated during serration is analyzed as to define shear bands dynamics characteristics.Depending on time, I shall present the use of nano-indention for investigating dynamics of nanoporous metallic materials deformation. N. Thurieau, L. Perriere, M. Laurent-Brocq, Y. Champion, J. Appl. Phys., 118 (2015) 204302. [more]

Topic day “Dislocation based plasticity – experiment vs. simulation” at “The Schöntal Symposium Dislocation-based Plasticity” of the DFG Forschergruppe FOR 1650

17674 1550059423

Topic day “Dislocation based plasticity – experiment vs. simulation” at “The Schöntal Symposium Dislocation-based Plasticity” of the DFG Forschergruppe FOR 1650

 
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