NMR Spectra of Hydroxyapatite Coatings

Information on the degree of disorder introduced by thermal treatment of hydroxyapatite during plasma spraying could be obtained by NMR spectroscopy. The positions and shift of 1H-MAS and 31P-MAS NMR peaks are indicative of the environment of the P043- tetrahedra in calcium orthophosphates and allow distinguishing between dehydroxylation (oxyhydroxyapatite) and decomposition (tricalcium phosphate, tetracalcium phosphate) products of hydroxyapatite. 

Phase Composition Nuclear Magnetic Resonance Spectroscopy I 327 

The inset shows the spectrum of a groups with single or paired OH- groups 

Additional work using 2D-double quantum 1H/31P cross polarisation heteronu-clear correlation (HETCOR) NMR spectroscopy confirmed that the phosphorous position D possibly represents an oxyapatite, Ca10(PO4)6O SRO structure (Hartmann et al., 2000). Because this chemical shift is identical to that of crystalline 

TTCP it can be concluded that with increasing dehydroxylation of oxyhydroxya-patite the Ca2+ and O2- coordination of the P043- tetrahedra as represented by the 31P D-band eventually approach those of TTCP, that is there exists a structural succession HAp - OHAp —OAp —TTCP (+TCP) as postulated earher. 

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