The research activities within the „Interface Structures and High-Temperature Reactions“ group focus on utilizing high-resolution structural techniques and aim at gaining mechanistic insight in processes, possibly on the atomic scale.
Staring form a surface science approach the group activities aim to bridge the complexity gap and pressure gap towards more realistic conditions of processes. This goal is achieved by studying still simplistic surfaces but in realistic environments such as electrolytes or corrosive gas atmospheres. In this line ideally ordered, single-element or (binary) alloy single-crystal surfaces but also systems such as complex, ideally disordered, i.e. homogeneously amorphous alloys are studied. Especially beneficial are in this context in-situ X-ray diffraction techniques using Synchrotron radiation, but also techniques such as Scanning Auger Electron Microscopy (SAEM) or Atom Probe Tomography. In particular the structural aspects accessed by in-situ X-ray diffraction are a valuable complementary addition to the department’s activities on electrochemical processes. Thus, although working on a broad scope of different subjects from oxide scale formation to Li-ion battery interfaces, the group’s main activities can be summarized as:
1. Using simplified (solid) model substrate systems such as single crystals, thin films, or amorphous/ nanocrystalline materials.
2. Employing high-resolution structural techniques such as in-house lab-based Auger Microscopy as well as Synchrotron-based large scale facilities - and possibly in-situ studies.
3. The main interest is in the behavior of systems in real atmospheres. In the focus are electrochemical interfaces and solid-gas reactions at elevated temperature.
Dealloying is a specific corrosion process and of large fundamental relevance in other electrochemical processes such as catalysis, too. In particular the binary alloy surface Cu3Au(111) with its very particular sequence of initial structural states [1,3,4] has been used within the group’s research program as a reference system to address the influence of corrosion accelerators [2,5,6] and of inhibition mechanisms [1,2]. Single crystal surfaces modified by self-assembled thiol monolayer films revealed a distinctive cracking failure mechanism with clear crystallographic crack openings, which opened a possibility to actually address the initial stages of crack formation in collaboration with other departments. As dealloying of noble metal alloys was also studied early-on in the context of stress corrosion cracking these results bear a large promise for furthering understanding in an ultimately technological context.
With corrosion of amorphous and nanocrystalline steels a further promising research topic could be established. Selective dissolution phenomena in the context of passivity and wet corrosion could be in great detail related to the respective nanostructured materials in collaborations with the Electrocatalysis group (Dr. K.J.J. Mayrhofer) and the Atom Probe Tomography group (Dr. P.-P.Choi, Department of Microstructure Physics and Metal Forming). This approach of using a unique set of complementary methods bears a great potential to actually gain deeper well-characterized insight into the microstructure-performance relation of corrosion reactions and passivity.
Next to further electrochemical reactions such as electrodeposition from ionic liquids (in collaboration with Dr. M. Rohwerder), phosphating (in collaboration with Dr. A. Erbe), or battery processes also elevated and high-temperature gas corrosion is studied in part with industrial partners in various atmospheres, i.e. oxidation, steam corrosion, or sulphidation. These works will be continued using more high-resolution methods and in-situ diffraction to study the initial stages of similar processes. The Fig. below includes two SAEM images showing the selective phosphate reaction on AS steel and a grain boundary prior to sulphidation.
 Pareek, A.; Borodin, S.; Bashir, A.; Ankah, G. N.; Keil, P.; Eckstein, G. A.; Rohwerder, M.; Stratmann, M.; Gruender, Y.; Renner, F. U.: Journal of the American Chemical Society 133, (2011) 18264-18271.
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 Ankah, G. N.; Pareek, A.; Rohwerder, M.; Renner, F. U.: Electrochimica Acta, (2012) DOI: 10.1016/j.electacta.2012.1008.1059.