The influence of initial glass powder particle size on the level of crystalline phase formation in apatite (C10(PO4)6(O,F2))-wollastonite (CaO-SiO2) (A-W) glass ceramic was investigated. Sample batches of A-W glass-ceramic were prepared with particle sizes ranging from 5 to 203 microns. The initial glass and glass-ceramic materials were analysed using particle size analysis, differential thermal analysis (DTA) and X-ray diffractometry (XRD). The DTA results demonstrated that the apatite peak remained constant whilst the smaller wollastonite phase peak gradually shifted towards the larger apatite peak. By 18 microns the two crystalline peaks were indistinguishable. XRD analysis displayed an increase in apatite towards 18 microns, decreasing thereafter with reduced particle size. Conversely, wollastonite was found to decrease towards 18 microns and then rapidly increase. The DTA and XRD results suggest that at a particle size at or around 18 microns, the mechanisms by which each of the two crystalline phases form my be altered, possible by an interchange between surface and bulk nucleation.
