Influence of phase separation on the devitrification of 45S5 bioglass.

The devitrification of the 45S5 variety of bioactive glasses (BGs) in relation to phase separation is studied with scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and positron annihilation lifetime spectroscopy techniques. It is shown that the type of phase separation (such as spinodal vs. droplet-like) has a pronounced effect on the activation energy of viscous flow and crystallization, the onset temperature of crystallization and the void size distribution at the nanoscale. Generally, the Johnson-Mehl-Avrami (JMA) relation does not describe crystallization kinetics in bulk 45S5 BG. However, for powder samples (<300 μm) the difference in crystallization kinetics, which is surface-driven for the two kinds of glasses, becomes much smaller, and can be described with the JMA relation under some circumstances.