Quantifying the effect of particle size on the crystallization of 45S5 bioactive glass

The crystallization behavior of 45S5 bioactive glass powders with two different particle sizes (<5 µm, BG5 and <32 µm. BG32) was investigated under non-isothermal conditions. The Ozawa and Augis-Bennett methods provided an Avrami coefficient close to 1 for both glass types, which suggests that surface crystallization was predominant during heat treatment. The Kissinger equation was used to determine the apparent activation energies for crystallization (Ec) that were found to be 250 ± 3 and 311 ± 9 kJ/mol for BG5 and BG32, respectively. The activation energies for viscous flow have also been assessed and were found higher than Ec (284 ± 8 and 338 ± 9 kJ/mol) for both particle sizes. It was noted that the process of crystallization for 45S5 glass could not be properly described by the Johnson-Mehl-Avrami (JMA) model and it appeared more complex than a simple nucleation-growth mechanism.