Influence of heat treatment on crystallization of bioactive glasses

In this work, the crystallization tendency of three bioactive glasses called bioglass 45S5, 1-98, and a new glass, 07-04 is discussed. The glasses were heat-treated in an electric laboratory furnace in nitrogen for different periods of time between 600 and 1000 °C, after which the samples were studied with SEM-EDXA and X-ray analysis. Glass 45S5 showed surface crystallization of sodium–calcium–silicate at 600 °C. At higher temperatures the glass crystallized homogenously. This suggests that also internal nucleation should be considered for 45S5. In glass 1-98 wollastonite nucleated in the surface around 800 °C. The thickness of the crystallized surface layer increased linearly with time and temperature of the heat treatment. The third glass 07-04 showed, depending on temperature, sodium–lime–silicate, diopside and wollastonite crystals. Sodium–calcium–silicate nucleated around 700 °C in the surface. With increasing temperature wollastonite and diopside formed simultaneously with sodium–calcium–silicate. At the highest temperatures the main crystalline type in the surface was diopside. The results indicate that sodium–calcium–silicate crystals nucleate and grow at lower temperatures than wollastonite or diopside crystals.