Nucleation and crystal-growth kinetics in ZrO2-strengthened Mica-glass-ceramics for dental application

A machineable mica based glass-ceramic for dental application has been developed. The main crystalline phase of the product is a Na-fluorophlogopite mica. The effect of ZrO2 addition on nucleation and crystallization was studied and the resulting microstructure was compared with the mechanical properties. No effective nucleation process was found in the zirconia-free composition. A constant number of crystals was found independent of the crystallization conditions. Therefore it is assumed that nuclei are quenched in during the preparation of the glass. A linear growth law for the mica crystals was found. Pseudodendritic growth forms seem to be the consequence of lattice defects. In contrast, the nucleation process of the ZrO2-containing glass is sensible to variations in composition and nucleation temperature. An optimized nucleation leads to a fine-grained mica structure after crystallization at 900°C. The fine-grained material has the highest mechanical strength and a lso better machineability and translucency. A second heating step may be applied to further strengthen the material, but translucency is decreased.