Predicting physical and chemical properties of bioactive glasses from chemical composition. Part 2: Devitrification characteristics

The tendency to devitrification was studied for 30 glass compositions in the range of interest for bioactivity (Na(2)O-K(2)O-MgO-CaO-B(2)O(3)-P(2)O(5)-SiO(2)). The glass transition and devitrification temperatures were determined by differential thermal analysis and hot stage microscopy. The crystal phases that formed were analysed by powder x-ray diffraction and SEM/EDXA. Depending on their alkaline oxide contents, the glasses tended to devitrify into wollastonite or sodium calcium silicate type crystals. The higher the alkaline oxide content, the lower was the devitrification temperature. Mathematical models describing the dependence of glass transition and devitrification temperatures on oxide composition were derived and successfully tested on four reference glass compositions. The models can be used to choose glass compositions with working properties suitable for specific high temperature processes.