Growth and modification of passive layers on new Zn alloys using atmospheric-pressure plasmas
Final Report Abstract
The project aimed to investigate the plasma treatment of technical heterogeneous ZnMgAl alloys by an atmospheric-pressure dielectric barrier discharge plasma. By this means, two 2D gradient plasma reactors were developed and successfully tested at the IOT, while at the TMC five plasma-induced changes on the surface were found and correlated to technical relevant adhesive and corrosive properties of the material. Although the heterogeneity of the material hindered a feasible performance of the 2D-gradient reactor within this project, the results gained at the IOT and the TMC deepened the understanding of surface processes in a dielectric barrier discharge plasma in general and specifically for the ZnMgAl interface. Specifically, the plasma gas composition was found to play a crucial role in the surface properties: Especially the addition of reactive species (hydrogen, oxygen, water) had shown to significantly alter the processes on the surface by on the one hand increasing certain processes such as the oxide layer growth but on the other hand decrease other processes such as the conversion of carboxylates to carbonates as well. In this regard, the addition of oxidizing species had shown to further improve the overall adhesive performance of the material, be it the wettability or the application of adhesives or self-assembled monolayers. In this manner, Ar + 5% H2O seemed to be a highly promising candidate for further applications. The time dependence of this plasma process yielded an increase in adhesive properties already after 5 seconds without the loss of its high corrosion resistance, allowing this plasma treatment to be implemented in a continuous in-line process. To deepen the understanding of the plasma processes taking place at the surface, a novel backside setup for insitu measurements was developed and successfully tested. With this setup, surface processes can be monitored in-situ with various methods such as DRIFTS and Raman spectroscopy. The setup was successfully applied to the plasma treatment of zinc oxide nanorods. Thereby, the evolution of defects in the semiconductor could be monitored by Raman spectroscopy in-situ, giving valuable insight into the surface reactions and kinetics. Additionally, a novel method to investigate plasma interactions with defined organic groups was introduced: By coating the surface with a self-assembled monolayer, the functional group in contact with the plasma could be predetermined. Combining this approach with the novel backside setup, a completely new way of understanding the plasma interactions of specific functional groups and reaction mechanisms can be gained. This approach was successfully tested using octadecyl phosphonic acid. To sum up, a thorough characterization of the plasma interaction with a ZnMgAl alloy and its following adhesive and corrosive properties was carried out that could lead to a technical applicable surface treatment process. The setups developed within this project will be transferred to other scientific issues, on the one hand allowing combinatorial approaches to accelerate scientific output on homogeneous samples and on the other hand deepening the understanding of plasma-surface interactions.
Publications
- Surface modification of ZnMgAl-coated steel by dielectric-barrier discharge plasma, RSC Advanced, 60, 35077-35088, Oct. 2019
S. Knust, A. Kuhlmann, T. de los Arcos and G. Grundmeier
(See online at https://doi.org/10.1039/c9ra07378g) - Organophosphonic acid monolayer adsorption on DBD plasma-treated ZnMgAl-alloy coated steel, Surface and Interface Analysis, April 2020
S. Knust, A. Kuhlmann, A.G. Orive, T. de los Arcos and G. Grundmeier
(See online at https://doi.org/10.1002/sia.6782) - Spray pyrolysis of thin adhesionpromoting ZnO films on ZnMgAl coated steel, Surface and Coating Technology
R. Grothe, S. Knust, D. Meinderink, M. Voigt, A. Orive, G. Grundmeier
(See online at https://doi.org/10.1016/j.surfcoat.2020.125869)
