Gel-to-ceramic conversion during hydroxyapatite synthesis

Conversion of hydroxyapatite (HA, Ca-10(PO4)(6)(OH)(2)) synthesis from gel to ceramic using solid-state nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction was studied. The Sol was prepared by dissolving calci um nitrate tetrahydrate and triethyl phosphate in 2-methoxyethanol. In soli d-state P-31 magic-angle spinning nuclear magnetic resonance (MAS NMR) spec tra, gel calcined at 250 degrees, 350 degrees, and 600 degreesC showed a co nversion from gel to glassy phosphate, then HA ceramic. Spin-lattice relaxa tion experiments of samples calcined at 600 degreesC indicated that the exi stence of a CaO impurity might affect (OHO)-O-... = PO3 linkages in a HA un it cell and result in longer P-31 spin-lattice time.