Preparation of bioactive Ti metal surface enriched with calcium ions by chemical treatment

A calcium solution treatment was applied to a NaOH-treated titanium metal to give it bioactivity, scratch resistance and moisture resistance. The titanium metal was soaked in a 5 M NaOH solution and then a 100 mM CaCl2 solution to incorporate Ca2+ ions into the titanium metal surface by ion exchange. This treated titanium metal was subsequently heated at 600 °C and soaked in hot water at 80 °C. The NaOH treatment incorporated ∼5 at.% Na+ ions into the Ti metal surface. These Na+ ions were completely replaced by Ca2+ ions by the CaCl2 treatment. The number of Ca2+ ions remained even after subsequent heat and water treatments. Although the NaOH–CaCl2-treated titanium metal showed slightly higher apatite-forming ability in a simulated body fluid than the NaOH-treated titanium metal, it lost its apatite-forming ability during the heat treatment. However, subsequent water or autoclave treatment restored the apatite-forming ability of the NaOH–CaCl2-heat-treated titanium metal. Although the apatite-forming ability of the NaOH-heat-treated titanium metal decreased dramatically when it was kept at high humidity, that of NaOH–CaCl2-heat-water-treated titanium metal was maintained even in the humid environment. The heat treatment increased the critical scratch resistance of the surface layer of the NaOH–CaCl2-treated titanium metal remarkably, and it did not deteriorate on subsequent water treatment.