The influence of calcium to phosphate ratio on the nucleation and crystallization of apatite glass-ceramics

The nucleation and crystallization behavior of a series of glasses based on 4.5SiO(2)- 3Al(2)O(3)-YP2O5-3CaO-1.51CaF(2) was studied. The parameter Y w as varied to give calcium to phosphate ratios between one and two. All of t he glasses studied crystallized firstly to fluorapatite (Ca-5(PO4)(3)F). Th e glass with a calcium to phosphate ratio of 1.67, corresponding to apatite , bulk nucleated to give fluorapatite (FAP). The glasses with calcium : pho sphate ratios either less than that of apatite, or greater than that of apa tite all exhibited surface nucleation of FAP. However, following a nucleati on hold of one hour at approximately 50 K above the glass transition temper ature these glasses exhibited bulk nucleation of FAP. (C) 2001 Kluwer Acade mic Publishers.