SOLID-STATE 31NMR STUDIES OF THE CONVERSION OF AMORPHOUS TRICALCIUM PHOSPHATE TO APATITIC TRICALCIUM PHOSPHATE

The hydrolytic conversion of a solid amorphous calcium phosphate of empirical formula Ca9(PO4)6 to a poorly crystalline apatitic phase, under conditions where Ca2+ and PO4(3-) were conserved, was studied by means of solid-state magic-angle sample spinning P-31-NMR (nuclear magnetic resonance). Results showed a gradual decrease in hydrated amorphous calcium phosphate and the formation of two new PO4(3-)-containing components: an apatitic component similar to poorly crystalline hydroxyapatite and a protonated PO4(3)-, probably HPO4(2-) in a dicalcium phosphate dihydrate (DCPD) brushite-like configuration. This latter component resembles the brushite-like HPO4(2-) component previously observed by P-31-NMR in apatitic calcium phosphates of biological origin. Results were consistent with previous studies by Heughebaert and Montel [18] of the kinetics of the conversion of amorphous calcium phosphate to hydroxyapatite under the same conditions.