Sintering behaviour of 45S5 bioactive glass

In this study, we report on the effect of Bioglass (R) structural transformations on its sintering behaviour. While heating up to 1000 degrees C, five successive transformations occur: glass transition, glass-in-glass phase separation, two crystallization processes and a second glass transition. The sintering of the material exhibits two main shrinkage stages associated with the two glass transitions at 550 and 850 C. At 580 degrees C, the glass-in-glass phase separation induces a decrease in the sintering rate immediately followed by the major crystalline phase crystallization (Na2CaSi2O6) between 600 and 700 degrees C, from the surface to the bulk of the particles. A complete inhibition of sintering takes place followed by a minor shrinkage effect due to crystallization. A plateau is then observed until the second glass transition temperature is reached. A modification of Frenkel's model allows the determination of the glass-in-glass phase separation kinetics and the identification of the structural transformations effects on sintering behaviour. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.