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

Abstract

Nucleation and crystallization behavior of fluor-mica fusion-cast ceramics has been investigated. By contrast to oxide glasses, fusioncast 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.