Effect of different gravity conditions on microstructure of glass melts within a stable miscibility gap

Abstract

On earth glass melts with a stable (liquid-liquid) immiscibility show a Sedimentation due to the effect of gravity on microphases with different densities. This results in stacked samples which consist of two layers. A microgravity experiment was carried out with a glass of the PbO-B₂O₃ system (within the liquid-liquid miscibility gap) to get samples with homogeneously distributed microphases. The glass was melted and cooled under microgravity conditions on board the Space stadon "MIR" using the "CSK-1 Kristallisator" furnace equipment. Electron microscopie investigations show the expected "undisturbed" (not stacked) immiscibility structure if gravity and Marangoni convection (both kinds of microphases have nearly identical surface tension [7]) do not have any influence on phase separadon. The basic principle established by this experiment can be applied to the preparation of partially crystallized glass composite materials by heterogeneous (induced) nucleation (noble-metal nuclei).