SURFACE STRUCTURE AND PROPERTIES OF CALCIUM HYDROXYAPATITE PARTICLES MODIFIED WITH PYROPHOSPHORIC ACID

Abstract

Synthetic colloidal calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: Hap) was treated with pyrophosphoric acid (H₄P₂O₇: PP) in acetone and the materials were characterized by a variety of techniques. XRD pattern and morphology of Hap particles were essentially not changed by the modification.The additional amount of PO₄ of Hap increased with an increase of PP concentration and the Ca/P molar ratio of the particles decreased from 1.62 to 0.8l. IR results indicated that the isolated surface P-OH band developed with increasing the PP concentration up to 6.0 mmol dm ^-3 by the reaction of isolated surface P-OH groups of Hap and PP. Above 10.2 mmol dm^-3, hydrogen-bonding surface P-OH band appeared at 2913 cm^-1 and enlarged with increasing the PP concentration, while the isolated surface P-OH band weakened. The results of N₂ and H₂O adsorption measurement revealed that the modified particles rather aggregated compared to the unmodified ones.