Solid-state phase transformation in a lithium disilicate-based glass-ceramic

The solid-state phase transformation in a lithium disilicate-based glass-ceramic (IPS e.max® CAD) was revisited on the basis of quantitative data. IPS e.max® CAD is widely used as material for the dental restoration in the dental industry. In-situ X-ray diffraction and differential scanning calorimetry accompanied by scanning electron microscopy observations were applied to understand phase transformation during heat treatment in a dental ceramic. In-situ X-ray diffraction evidences the concomitant formation of cristobalite and lithium orthophosphate at 770 °C. Then, the formation of lithium disilicate occurred at the expense of a complete dissolution of cristobalite and lithium metasilicate. No phase transformation occurred during cooling. The quantitative results of microstructural features (amount of each phase, morphology, and number density of lithium disilicate and lithium metasilicate) indicate that lithium disilicate is probably formed by diffusional process at the lithium metasilicate/cristobalite interface, which acts as favorable nucleation sites. The energy barrier is probably too high for lithium disilicate nucleation in the amorphous matrix. The quantitative results will provide the background for further modeling of phase transformation kinetics, which may have potential industrial benefits.