Real-time small-angle neutron scattering (SANS) and neutron diffraction (ND) studies have been performed on a calcium fluorapatite (Ca 5 (PO 4 ) 3 F) (FAP) glass-ceramic composition. The cast glass exhibited scattering at low q and a peak in I(q) at higher q. The scattering at low q is thought to arise from a larger-scale nucleated structure, while the peak in I(q) is thought to arise from a finer spinodally decomposed structure. High temperature viscoelastic measurements show two reductions in the storage modulus (E 0 ) and two peaks in the damping factor (tan d) consistent with a glass that has undergone amorphous phase separation (APS) during the casting process. On heating to 7801C, the scattering at low q increased in intensity, while the peak in I(q) increased in intensity and moved to lower q, consistent with the coarsening of the finer scale phase separated structure. During isothermal experiments, the scattering at low q increased in intensity and the peak in I(q) moved to lower q, corresponding to a final spacing of about 35 nm. After about 30 min at 7401C, and 12 min at 7501C the coarsening process effectively stopped and is inhibited by the glass transition temperature (T g ) of the second glass phase. ND showed the glass to crystallize on heating to FAP and then mullite (2SiO 2 . 3Al 2 O 3 ). At high temperatures, both the FAP and mullite crystal phases partially re-dissolved, but were found to re-crystallize rapidly on subsequent cooling. The results indicate that the proposed crystal growth hold is actually a crystal dissolution hold, with recrystallization occurring rapidly on cooling. The results indicate that it is important to control not only the heat-treatment cycle but also the cooling cycle.

Strontium is one of the most common substituents in apatite crystals. The presence and behavior of Sr in apatite-group phases are of considerable significance in biology. The present paper investigates the substitution of strontium for calcium in a glass-ceramic of the following composition 4.5SiO23Al2O31.5P2O54CaO1CaF2. The glasses were characterized using Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), neutron diffraction (ND) and 19F Resonance Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR). The all calcium glass crystallized to calcium fluorapatite (Ca5(PO4)3F). Substituting strontium partially for calcium resulted in the formation of a mixed strontium/calcium fluorapatites. In contrast complete substitution resulted in the formation of strontium fluorapatite. MAS-NMR showed the the F to be present as F-Ca(3) representing a fluoride ion surrounded by three Ca2+ ions in the all calcium glass and was present as F-Sr(3) in the all strontium glass. In the mixed glasses fluorine was present as FCa( 3), F-Ca(2)Sr, F-CaSr(2) and F-Sr(3). Ca had a higher tendency to occupy the F-M(3) sites than Sr which may reflect the higher charge to size ratio of Ca2+ relative to Sr2+ and its greater affinity for F- ions.

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