Effect of dehydration on structure and induction capability for apatite formation of microarc oxidized TiO2-based film with chemical modification

A microarc oxidized (MAO) TiO2-based film containing Ca and P was prepared on titanium alloy. The structure and apatite-forming ability of the MAO film before and after chemical treatment (NaOH aqueous solution) and subsequent dehydration at 400 and 600 °C were investigated. Before and after dehydration, the surface of the chemically etched MAO film show the presence of anatase and amorphous phase with a honeycombed morphology composed of numerous nano-flakes (50–100 nm in thickness) and pores (100–200 nm in size). The apatite-forming ability of the MAO film was improved greatly after chemical etching; however, that of the etched MAO film decreases after dehydration. The reason for this is that dehydrated Ca–Ti–O compounds on the surfaces of the etched and heat-treated MAO films are unfavorable for Ca ions release compared with the hydrous Ca–Ti–O compound on the surface of the etched MAO film. The decreased ability of Ca2+ ions release further lowers the formation ability of Ti–OH groups produced via ionic exchange between Ca2+ ions of the etched and heat-treated MAO films and H3O+ ions in simulated body fluid.