Effects Kind of Nucleation Agent Particle Size on the Crystalline Phases and Microstructure of Glass-Ceramics for Dentistry Applications

The objective of the study was to evaluate the effects of nucleation agent particle size on the properties of lithium disilicate glass ceramics for dentistry applications. In order to achieve this aim، the TiO2-ZrO2-Li2O-CaO-Al2O3-SiO2 system was investigated by incorporation of P2O5 and Nb2O5 as nucleation agent. Raw materials were melted and glass heat treated at different temperatures ranging from 500-900ºC to produce glass-ceramic with the lithium disilicate major crystalline phase. In the end، flexural strength and micro hardness of the samples were studied. Then، the size of P2O5 particles was changed to the size of nano particles and the effects of nucleation agent particle size on the properties of the glass-ceramics were discussed. The change of nucleation agent particle size to nano size resulted in decreasing the nucleation temperature، the changing morphology of Li2Si2O5 crystals from needle-shaped to spherical-like، the increasing volume fraction of the lithium disilicate major crystalline phase، the decreasing volume fraction of the minor and middle phases and the optimizing of mechanical properties. In the next step، Nb2O5 was used as a nucleating agent. The changing of nucleation agent resulted in the changing kind of crystalline phases and microstructure and the changing of crystallization mechanism from volume to surface. In this step، due to the crystalline phase''s directional crystallization and coarsening، many cracks were observed in these samples. By using the nucleating agent Nb2O5، the major crystalline phase became spodumene