Effects of anodization voltage on CaP/Al2O3–Ti nanometre biocomposites

Nanometre CaP/Al2O3–Ti biocomposites for implant applications were successfully fabricated using a hybrid technique of anodization and hydrothermal treatment, in which CaP/Al2O3 formed a double-layer coating on titanium with porous CaP as the top layer and anodic Al2O3 film as the intermediate layer. Techniques, such as x-ray diffraction (XRD), electron scanning microscopy and energy disperse x-ray analysis (SEM + EDX), transmission electron microscopy (TEM) and atomic force microscopy (AFM), were used to investigate the composition, microstructure and morphology of the fabricated CaP/Al2O3 composite coating and the CaP/Al2O3–Ti biocomposites. XRD results showed that the fabricated composite coating contained Al2O3 and various calcium phosphate phases. SEM and TEM micrographs confirmed that CaP crystals were in nanometres, embedded in situ in the walls of the cylindrical structure of anodic alumina, and finally formed a thin and porous top layer on the anodic alumina intermediate layer. The nanometre and T-shape effects of the CaP top layer, and the porous and cylindrical microstructure of CaP/Al2O3 composite coating could produce an excellent combination of bioactivity and mechanical integrity of the CaP/Al2O3–Ti biocomposites. It was also found that the anodization voltage of the anodization process played an important role on the composition and microstructure of the fabricated CaP/Al2O3–Ti biocomposites. The contents of Ca and P incorporated in anodic alumina depended strongly on the anodization voltage. Their variations could result in different CaP phases, CaP crystal shapes and sizes, and topography of the CaP/Al2O3–Ti biocomposites. The optimal anodization voltage in this study was found to be in the range 40–60 V.