Characterization and Bioactivity in High Cristobalite-Nepheline-Apatite Glass and Glass Ceramics

Abstract

Within the Na2O-CaO-Al2O3-SiO2-P2O5-F system, in the nominal binary nepheline-fluorapatite phases were prepared and investigated. Transparent glasses were obtained in a high nominal ratio of nepheline, i.e. 75, 80, 85 and 90%, whereas the low ones, i.e. 25, 50 and 70% gave devitrified glasses. The thermal behaviour of the glasses and both the crystalline phases and the microstructure of the glass ceramic were investigated. Moreover, the bioactivity of glasses and glass ceramics was also examined. Nepheline, fluorapatite and high cristobalite were the main crystalline phases developed through the heat-treatment process of the glass powders in the 800–1250°C temperature range. High cristobalite and nepheline were developed as the main phases that were treated either at high or low temperature. The microstructure shows spread crystals and flake-like crystals embedded in a glassy matrix. In vitro, the bioactivity testing of the glasses and the corresponding glass-ceramic, sintered at 900°C, showed that the sample containing 75% nominal nepheline was the best regarding in the bioactivity behaviour.