Nucleation and growth of needle-like fluorapatite crystals in bioactive glass–ceramics

The nucleation behaviors of glass–ceramics with different Ca–mica (Ca_0.5Mg₃AlSi₃O₁₀F₂)/fluorapatite ratios were investigated. By using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscope with an energy dispersive spectrometer (SEM/EDS), the effect of CaO and P₂O₅ addition on the nucleation behaviors was studied. Results showed that the addition of CaO and P₂O₅ promoted nucleation process and led to the formation of different nucleation phases. After further heat treatment, Ca₅(PO₄)₃F crystals were of needle-like morphology, instead of particle-like reported in previous studies. This can be attributed to the one-dimensional rapid growth of fluorapatite along the c-axis. The values of the Avrami parameter, n, and the dimensionality of crystal growth, m, are found to be 2 and 1, respectively, which indicated that the bulk nucleation is the dominant mechanism in crystallization, and one-dimensional growth of fluorapatite is preferred. Since needle-like fluorapatite crystals are of the same morphology to hydroxyapatites in human bones, the glass–ceramics thus prepared show excellent bioactivity in vivo.