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 mu m, BG5 and <32 mu m. 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 (E-c) 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 E-c (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. (C) 2018 Elsevier B.V. All rights reserved.