Calcium-hydroxide slurry processing for bioactive calcium-titanate coating on titanium

The present study investigates the relationships between the treatment conditions and characteristics of the surface layer in a surface treatment process using calcium-hydroxide slurry. Furthermore, the appropriate treatment conditions for preparing the bioactive coating are also investigated by soaking the specimens in a simulated body fluid. The treatment process using calcium-hydroxide slurry is as follows: a titanium substrate is buried in calcium hydroxide slurry, and the slurry is then heated at 873 K in air. The calcium hydroxide slurry was prepared by mixing 1 g of calcium hydroxide powder per 1, 1.2, 1.5, or 2 mL of water. The slurry was heated to 873 K with various heating rates from 100 to 600 K h^{- 1} and held at 873 K for 1 and 2 h. As the ratio of water in the slurry increased or the heating rate decreased, the atomic ratio of calcium to titanium in the surface layer decreased. A surface treatment using slurry containing a mixture of 1.0-mL water per 1.0-g calcium hydroxide powder, a heating rate of 600 K h^{- 1}, and a holding time of 2 h produces a crystallized stoichiometric calcium titanate layer on the titanium substrate. Treatment using slurry of a higher water ratio or a slower heating ratio results in the formation of a dioxide layer containing locally formed calcium titanate. On the crystallized calcium titanate layer, calcium phosphate is formed faster in a simulated body fluid than in the TiO₂ layer containing calcium titanate; therefore, the treatment conditions forming the crystallized calcium titanate layer are appropriate for the bioactive coating.