Nucleation Kinetics of Lithium Metasilicate in ZrO2-Bearing Lithium Disilicate Glasses for Dental Application



The effect of ZrO2 on the nucleation of lithium metasilicate crystals in lithium disilicate-based multicomponent glasses of composition in wt% x ZrO2 + (1 − (x/100)) (73.82 SiO2 + 3.99 K2O + 15.33 Li2O + 3.51 Al2O3 + 3.35 P2O5) with = 0, 3, 4, 6, 8, and 12 was studied by combining the results from differential scanning calorimetry (DSC), micropenetration viscometry (MPV), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Peak shift of the first exotherm of DSC upscans indicated an increase in the temperature of maximum nucleation from 793 K (= 0) to 873 K (= 12), while number densities of relict structures of SEM images after nucleation at these temperatures and etching with HF led to an increase in the maximum nucleation rate from 2 × 1017/m3s (= 0) to 6 × 1018/m3s (= 12). MPV showed that viscosity increased with the ZrO2 content but nucleation was fastest close to 109.7 Pa s for all glasses studied. XRD revealed lithium metasilicate crystals within the etched volumes of approximately one order of magnitude smaller sizes compared to SEM relict structures, which were assumed to result from early-stage phase separation and heterogeneous nucleation processes.