Crystallization kinetics, mineralization and crack propagation in partially crystallized bioactive glass 45S5

Thermal treatment of bioactive glass ceramics dictates many important features such as microstructure, degree of crystallinity, mechanical properties, and biological response. This report investigates the heat treating conditions and the Avrami crystallization kinetics of melt cast bioactive glass 45S5 at 680 degrees C. Glass discs were found to follow three dimensional bulk crystallization kinetics (Avrami exponent n = 3). Partially crystallized bioactive glass samples were subjected to in vitro immersion testing to assist a comparative study of the adhesion capabilities of the mineralized layer formed on crystalline and amorphous regions. Higher adhesion of the mineralized layer to the amorphous region was observed as compared to its crystalline counterpart. Furthermore, Palmqvist crack propagation in amorphous and partially crystallized bioactive glass was studied. The crack paths in amorphous bioactive glass were straight, yet crack deflections were observed in the crystalline regions, likely attributed to different crystallographic orientations of crystals or residual thermal mismatch strains present in the bioglass ceramic. Hence, the mineralized layer interfacial fracture toughness and bulk fracture toughness of bioglass ceramics are different from their amorphous counterpart. (C) 2010 Elsevier B.V. All rights reserved.