Surface or internal nucleation and crystallization of glass-ceramics

Abstract

Fluoroapatite (Ca5(PO4)3F) was precipitated in glass-ceramics via internal crystallization of base glasses. The crystals grew with a needle-like morphology in the direction of the crystallographic c-axis. Two different reaction mechanisms were analyzed: precipitation via a disordered primary apatite crystals and a solid state parallel reaction to rhenanite (NaCaPO4) precipitation. In contrast to the internal nucleation used in the formation of fluoroapatite, surface crystallization was induced to precipitate a phosphate-free oxyapatite of NaY9(SiO4)6O2-type.Internal nucleation and crystallization have been shown to be a very useful tool for developing high-strength lithium disilicate (Li2Si2O5) glass-ceramics. A very controlled process was conducted to transform the lithium metasilicate glass-ceramic precursor material into the final product of the lithium disilicate glass-ceramic without the major phase of the precursor material. The combination of all these methods allowed the driving forces of the internal nucleation and crystallization mechanisms to be explained. An amorphous phosphate primary phase was discovered in the process. Nucleation started at the interface between the amorphous phosphate phase and the glass matrix.The final products of all these glass-ceramics are biomaterials for dental restoration showing special optical properties, e.g. translucence and color close to dental teeth.