Particle size effects on apatite-wollastonite glass crystallisation

The influence of initial glass powder particle size on the level of crystal line phase formation in apatite (Ca-10(PO4)(6)(O,F-2))-wollastonite ((CaOSi O2)-Si-.) (A-W) glass-ceramic was investigated. Sample batches of A-W glass -ceramic were prepared with particle sizes ranging from 5 to 203microns. Th e initial glass and glass-ceramic materials were analysed using particle si ze 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 a patite peak. By 18microns the two crystalline peaks were indistinguishable. XRD analysis displayed an increase in apatite towards 18microns, decreasin g thereafter with reduced particle size. Conversely, wollastonite was found to decrease towards 18microns. and then rapidly increase. The DTA and XRD results suggest that at a particle size at or around 18micr ons, the mechanisms by which each of the two crystalline phases form may be altered, possibly by an interchange between surface and bulk nucleation.