Influence of MoO3 and ZrO2 on the crystallization of fluor-mica fusion-cast ceramics

Nucleation and crystallization behavior of fluor-mica fusion-cast ceramics has been investigated. By contrast to oxide glasses, fusion-cast ceramics based on potassium or barium fluor micas display a strong tendency to volume nucleation. For some specific compositions belonging to the latter group, the addition of MoO3 and ZrO2 has been studied. MoO3 was selected because it is known to promote homogeneous nucleation by lowering the surface energy difference between melt and crystals, and ZrO2 was selected because it is a classical nucleation catalyst in many glass-ceramic systems. It is shown that both additives substantially reduce the crystallization rates and also cause concomitant changes in the resulting ceramic microstructures. Both effects are interpretated as a consequence of increased melt viscosity. An effect of nucleus formation promoted by MoO3 is not observed.