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Media type:
E-Article
Title:
Crystallization Mechanism of the Bioactive Glasses, 45S5 and S53P4
Contributor:
Massera, Jonathan;
Fagerlund, Susanne;
Hupa, Leena;
Hupa, Mikko
imprint:
Wiley, 2012
Published in:Journal of the American Ceramic Society
Language:
English
DOI:
10.1111/j.1551-2916.2011.05012.x
ISSN:
1551-2916;
0002-7820
Origination:
Footnote:
Description:
<jats:p>The crystallization kinetics of the two commercial bioactive glasses, 45S5 and S53P4, was studied using differential thermal analysis (<jats:styled-content style="fixed-case">DTA</jats:styled-content>), optical microscopy, and scanning electron microscopy (<jats:styled-content style="fixed-case">SEM</jats:styled-content>). The thermal properties, the activation energy of crystallization, and the Johnson‐Mehl‐Avrami (<jats:styled-content style="fixed-case">JMA</jats:styled-content>) exponent were determined for two glass fractions: fine powder (<45 μm) and coarse powder (300–500 μm). The crystallization behavior of 45S5 was significantly different for the two fractions, whereas the particle size did not affect the crystallization behavior of S53P4. The <jats:styled-content style="fixed-case">JMA</jats:styled-content> exponent of S53P4 suggested surface crystallization for both size fractions. However, for 45S5, the <jats:styled-content style="fixed-case">JMA</jats:styled-content> exponent suggested that, with increasing particle size, crystallization evolves from predominantly surface crystallization to predominantly bulk crystallization. Surprisingly, <jats:styled-content style="fixed-case">SEM</jats:styled-content> imaging did not support this conclusion. A method based on the crystallization rate dα/dt showed that the <jats:styled-content style="fixed-case">JMA</jats:styled-content> approach could not be employed for 45S5. The crystallization mechanism of 45S5 appears to be more complex than a simple nucleation and growth process. Nucleation‐like curves were measured for both fractions of the two glasses. The maximum nucleation rate occurred at 566 ± 4°C and 608 ± 4°C for the coarse powders of 45S5 and S53P4, respectively. The higher maximum nucleation temperature of S53P4 was attributed to the higher SiO<jats:sub>2</jats:sub> content. The nucleation temperature range of these two glasses together with <jats:styled-content style="fixed-case">DTA</jats:styled-content> data makes it possible to develop guidelines for tailoring thermal treatment parameters to achieve desired glass‐to‐crystal ratios.</jats:p>