TY - CONF A1 - Reinsch, Stefan A1 - Tielemann, Christopher A1 - Busch, R. A1 - Patzig, C. A1 - Müller, Ralf A1 - Höche, T. T1 - Oriented surface crystallization in 18BaO·22CaO·60SiO2 and MgO·CaO·2SiO2 glasses N2 - Up to now, oriented surface crystallization phenomena are discussed controversially, and related studies are restricted to few glasses. The vast majority of previous work does not consider possible effects of surface preparation and surrounding atmosphere. Moreover, very few observations of surface crystal orientation were made on separately grown crystals. The aim of our project is to advance the basic understanding of oriented surface crystallization, e.g. whether preferred orientation of surface crystals results from oriented nucleation or reorientation mechanisms during early crystal growth. In both cases, crystal orientation may reflect the orientation of the glass surface or that of anisotropic active surface nucleation sites. Therefore, we focus on orientation of surface crystals separately growing under controlled conditions. First results on diopside (MgCaSi2O6) and walstromite (BaCa2Si3O9) crystals growing from 18BaO·22CaO·60SiO2 and MgO·CaO·2SiO2 glass surfaces, respectively, indicate that different orientation mechanisms may occur. Neighbored walstromite crystals were found to gradually reorient themselves when they are going to impinge each other during stepwise isothermal treatments (log η = 4,5 Pa*s) of polished glass samples. Nevertheless, no preferred crystal orientation was evident for separate crystals. For diopside crystals growing from polished glass surfaces (1 μm diamond lapping foil), strong preferred orientation was observed for 3.5 to 85 min annealing at 850 °C. Electron Backscatter Diffraction (EBSD) studies showed that the c-axis of surface crystals is oriented parallel to the glass surface and that separated diopside crystals as small as 600 nm are already oriented. Studies on glass surfaces, polished with diamond lapping foils starting from 16 μm down to 1 μm grain, revealed that crystal orientation may scatter arround this preferential orientation and that this scatter progressively decreases with decreasing polishing grain size. T2 - 93rd Annual Meeting of the German Society of Glass Technology (DGG) in conjunction with the French Union for Science and Glass Technology (USTV) Annual Meeting CY - Nuremberg, Germany DA - 13.05.2019 KW - Surface crystallization KW - Orientation KW - Glass KW - Diopside PY - 2019 AN - OPUS4-48198 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Scheffler, F. A1 - Fleck, M. A1 - Santiago, C. F. A1 - Brauer, D. S. A1 - Müller, Ralf T1 - Morphologies of Fresnoite surface crystals of BT0.75S glass under different atmospheric conditions N2 - Fresnoite glass-ceramics are characterized by piezoelectric, pyroelectric and non-linear optical properties. These properties can be adjusted by orienting the fresnoite crystals during crystallization. Crystallization begins at the surface. The first surface crystals are not oriented perpendicular and, therfore, produce a surface layer that has not the intended properties. To overcome this issue, the formation of fresnoite surface crystals at different atmospheric conditions was studied. T2 - 9th Int. Otto Schott Colloquium CY - Jena, Germany DA - 09.09.2019 KW - Glass KW - Surface crystallization KW - Crystal orientation PY - 2019 AN - OPUS4-50460 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -