MICROSTRUCTURE OF MICA GLASS-CERAMICS AND INTERFACE REACTIONS BETWEEN MICA GLASS-CERAMICS AND BONE

This review paper characterizes glass-ceramics containing mica as main crystal phase. The phase formation reactions in dependence of the chemical composition and the microstructure are shown. Microstructure of mica glass-ceramics has been studied by electron replica and scanning electron microscopic (SEM) techniques. Mica glass-ceramics have previously been developed in SiO2-B2O3-Al2O3-MgO-F--base glasses. The material is machinable because of the precipitation of micas of fluorophlogopite-type. Also, a machinable glass-ceramic for dental applications was developed based on KMg2.5(Si4O10)F2-micas. We developed mica glass-ceramics in the SiO2-Al2O3-MgO-Na2O-K2O-F glass system. Phase formation within these glasses was observed by SEM. A double controlled nucleation and crystallization of mica and apatite crystals was possible in glasses of the SiO2-MgO-Na2O-K2O-F-CaO-P2O5-(Al2O3) system. The main crystal phases of phlogopite-type were characterized by SEM and energy dispersive x-ray spectroscopy (EDS) and apatite crystals Ca5(PO4)3(OH,F) were analyzed by X-ray diffraction measurements. The glass-ceramics are useful biomaterials for bone substitution. EDS analysis shows the ion exchange between glass-ceramics and body fluids. The interface reaction is characterized by formation of a small phosphate layer, and particularly by alkali ion exchange.