Water on Calcite (10.4) and K-Feldspar (001) - Adsorption Structure and Desorption Kinetics -

Mineral-water interfaces are omnipresent in nature and, thus, they play a decisive role in many environmental processes such as biomineralization, weathering of rocks, and atmospheric ice nucleation by mineral dusts. These small-scale processes at mineral-water interfaces have tremendous impact on our environment. For instance, ice nucleation caused by mineral dusts changes the properties of clouds, and, thus, influences our weather and climate. Consequently, a detailed molecular-level understanding of mineral-water interfaces is crucial to understand and model our environment.<br /> In this thesis, the mineral-water interactions of two particularly interesting mineral surfaces, calcite (10.4) and K-feldspar (001), are investigated. Calcite is the most abundant carbonate mineral in the Earth’s crust. Despite its abundance, a central surface property, the presence of a surface reconstruction, remained elusive so far. Only recently, an atomic force microscopy (AFM) study has provided convincing evidence for a (2 x 1) reconstruction at 5K. However, it remained unclear whether this reconstruction persists at room temperature and how it a↵ects the interaction of calcite with its environment. Here, temperature programmed desorption (TPD) experiments of water and ethanol desorbing from calcite (10.4) at ambient temperatures are presented. The desorption curves of both molecules exhibit a double-peak structure, which can be explained excellently by a kinetic model considering two types of adsorption sites as expected for a (2 x 1) reconstructed surface. Thus, this thesis provides evidence that the (2⇥1) reconstruction not only exists at room temperature but has significant impact on the interfacial properties of calcite. <br /> K-rich feldspar minerals are one of the most important ice nuclei under mixedphase cloud conditions, but the mechanism behind their exceptional ice nucleation activity is still unknown. In this thesis, high-resolution AFM data taken at the (001) surfaces of K-feldspars microcline and adularia under ultrahigh vacuum conditions are presented. On both minerals, AFM images reveal a nanostructure with a high density of step edges, and — in case of microcline — islands on the terraces and at the step edges. Based on atomic-resolution images, the islands on microcline were identified as intrinsic surface features. For both mineral surfaces atomic structures are revealed that are consistent with a hydroxyl-terminated surface, suggesting that the feldspar surface readily reacts with residual water in the experimental setup. These results establish a solid understanding of the pristine feldspar surface as required for unraveling the mechanism of ice nucleation on feldspar minerals. <br /> In conclusion, this thesis provides detailed insights into the molecular-level interactions of water with two important mineral-water interfaces and, thus, it deepens our understanding of mineral-water interactions in general.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bielefeld

Year

2023

Author dc:creator

• Dickbreder, Tobias

Repository record source_url

https://pub.uni-bielefeld.de/record/3006308

OAI identifier oai:identifier

oai:pub.uni-bielefeld.de:3006308