Direct observation of the liquid miscibility gap in the zirconia–silica system

In the technically important ZrO2–SiO2 phase system we studied liquid phase formation and solidification by means of the containerless aero acoustic levitation preventing contamination by contact to crucible material. The behaviour of the melt was recorded by a high-speed camera allowing for direct observation of convection, formation and solidification of emulsified reams. For the first time since 1956, we re-treated the liquidus miscibility gap between 59.5 mol-% and 78 mol-% SiO2 at 2250 °C with the critical point at 2430 °C and 70 mol% SiO2. Quenching preserved primary microstructures of the monotectic equilibrium with ZrO2-dendrites in a matrix of silica glass and secondary ZrO2 but also frozen-in Bénard-Marangoni cell patterns of metastably undercooled of emulsified droplets. These microstructures remind to the partitioning and coagulation behaviour of alkali-borosilicate glasses.