Influence of the Ca/P ratio on the morphology of fluorapatite crystals in SiO2–Al2O3–CaO–P2O5–K2O–F− glass-ceramics

The formation of fluorapatite crystals with needle-like morphology was studied in glass-ceramics (GCs) of the system SiO2–Al2O3–CaO–P2O5–K2O–F−. X-ray diffraction (XRD), 31P and 27Al nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), temperature-dependent electric conductance measurements, and transmission electron microscopy (TEM) with energy dispersive X-ray analysis were used to study the influence of the Ca/P ratio of the starting glass composition on the apatite crystal morphology. The composition of the ambient glass hosting apatite crystals and particularly the calcium supersaturation herein is shown to be the key to an understanding of the apatite crystal morphology observed.