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 deve loped. The main crystalline phase of the product is a Na-fluorophlogopite m ica. The effect of ZrO2 addition on nucleation and crystallization was stud ied and the resulting microstructure was compared with the mechanical prope rties. No effective nucleation process was found in the zirconia-free compo sition. A constant number of crystals was found independent of the crystall ization conditions. Therefore it is assumed that nuclei are quenched in dur ing the preparation of the glass. A linear growth law for the mica crystals was found. Pseudodendritic growth forms seem to be the consequence of latt ice defects. In contrast, the nucleation process of the ZrO2-containing gla ss is sensible to variations in composition and nucleation temperature, An optimized nucleation leads to a fine-grained mica structure after crystalli zation at 900 degreesC. The fine-grained material has the highest mechanica l strength and also better machineability and translucency. A second heatin g step may be applied to further strengthen the material, but translucency is decreased.