SURFACE MODIFICATION OF MIXED HYDROXYAPATITES Ca(10-x)Nix(PO4)6(OH)2 BY GRAFTING PHENYL PHOSPHONIC DICHLORIDE

Solid solutions of calcium-nickel hydroxyapatites Ca(10-x)Nix(PO4)(6)(OH)(2) with 0 <= x <= 2 were obtained by precipitation at pH=11. The surface of mixed apatite has been modified by reacting with different amounts of phenyl phosphonic dichloride C6H5POCl2 (PPO). Surface modification is attested by X-ray diffraction, IR and P-31 MAS-NMR spectroscopies, chemical and thermogravimetric analysis. After reaction with PPO, X-ray powder analysis shows the conservation of the apatite structure with formation of new phases, monetite (CaHPO4) and brushite (CaHPO4 center dot 2H(2)O). IR spectra display the vibration modes of PO43- and OH- groups and new vibration modes related to phosphonate groups appear essentially at 2950, 1440, 770, 720 and 696 cm(-1). The P-31 MAS-NMR spectra exhibit new signals, assigned to the presence of organic phosphorus. According to these results, a mechanism is proposed for the formation of two types of covalent bonds between the organic reagent and the superficial hydroxyl groups of the apatite ( CaOH) and ( POH).