Heidelberg 2015 – wissenschaftliches Programm
UP 4.23: Poster
Mittwoch, 25. März 2015, 10:45–19:45, G/Foyer
Ice crystal growing on mineral surfaces in ESEM — •Felix Bachmann1, Alexei Kiselev1, Philipp Pedevilla2, Stephen Cox2, and Angelos Michaelisdes2 — 1Atmospheric Aerosol Research Department, Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany — 2London Centre for Nanotechnology, University College London, London, UK
Observing deposition growth of ice crystals in an Environmental Scanning Electron Microscope (ESEM, FEI Quanta 650 FEG), we noticed that the ice crystals often have identical orientation of both basal and prism faces, and are tilted at a universal angle of 116° to the surface of the mineral substrate. To determine the range of conditions favoring such alignment, we have tested temperatures from -25°C to -50°C with freshly cleaved and weathered mineral surfaces. These experiments have been realized with our self-build humidity control system which allowed us to control partial water vapor pressure in the ESEM chamber. Alignment of crystals requires that the c-axis of both ice and microcline crystal lattice have to be parallel but also means that the basal (001) planes of ice and microcline are mismatched. We report a gradual reduction of crystal alignment with decreasing temperature. We discuss a possible mechanism of crystal lattice alignment by considering a layer of ordered water on the surface of microcline forming prior to ice nucleation. Using DFT we show how the mineral surface interacts with water, particularly addressing the role of surface cations and hydroxyl groups in the arrangement of adsorbed water molecules.