Apatite-wollastonite glass-ceramics. I. Crystallization kinetics by diffreential thermal analysis

Bioactive apatite-wollastonite (A-W) glass-ceramics exhibit high fracture toughness and strength, which allow them to be used as load-bearing implants. Formation of a wollastonite phase upon appropriate heat treatment is responsible for the substantial increase in mechanical properties. However, crystallization of the wollastonite phase creates defects, such as pores, cracks, etc., and in the worst case, even breaks a bulk sample. Details on crystallization kinetics of this glass system have not been published. The DTA studies show the strong effect of glass particle size on the crystallization temperature of the wollastonite phase. Apatite crystallization in the apatite-wollastonite glass exhibits a three-dimensional bulk mechanism with an Avrami parameter (n)approx =3, while that of the second phase (wollastonite) shows a two-dimensional surface mechanism (planar growth) with napprox =2. A strong effect of glass particle size on the wollastonite crystallization temperature is observed. The peak temperature is lower when the particle size is smaller.