Polished pieces of a glass with the composition 2BaO·TiO 2 ·2.75SiO 2 (fresnoite + 0.75SiO 2 ) 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. Insitu 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.

No abstract