Structural characterization of nanostructured hydroxyapatite–iron oxide composites

Abstract Nanostructured hydroxyapatite (HA)–iron oxide composites obtained by a wet-chemical method through co-precipitation were investigated with respect to the changes induced in the samples structure by progressive addition of iron, by thermal treatments carried out at 450 °C, 550 °C and 700 °C, and by incubation in simulated body fluid. The structural changes were analyzed by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and magic angle spinning nuclear magnetic resonance (MAS-NMR). After heat treatments, crystalline HA was developed in all samples, even in larger amount in those with iron, showing that iron acts as a catalyzer for HA development. The MAS-NMR results show as well that only a part of the iron atoms are uniformly incorporated in the HA structure by replacing calcium. EPR results support that an important part of iron atoms are disposed in regions rich in iron that behave like superparamagnetic or magnetic particles distributed in HA matrix. The analyses carried out on 550 °C treated samples, after three days of immersion in SBF, point out a decrease of HA crystallite size and the appearance on particles surface of a new amorphous calcium phosphate layer.