Surface Crystallization of Fresnoite from a Glass Studied by Hot Stage Scanning Electron Microscopy and Electron Backscatter Diffraction

Abstract

Polished pieces of a glass with the composition 2BaO·TiO2·2.75SiO2 (fresnoite + 0.75SiO2) were annealed at 790–970 °C and subsequently analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD). Surface morphologies and textures of samples annealed in a normal furnace are presented. While the texture of oriented nucleation occurs over the entire temperature range, the development of previously undetected secondary textures is described and explained. In-situ high temperature video sequences visualize the growth and a two-step nucleation of fresnoite. The velocity of crystal growth along the surface in the vacuum is measured and compared to the mean velocity of three-dimensional crystal growth in an ambient atmosphere. For example, growth velocities along the surface reach 3.6 μm/min in the vacuum at 830 °C compared to 0.16 μm/min during growth into the bulk.