Application of carbonated apatite coating on a Ti substrate by aqueous spray method

The fabrication and characterization of a carbonate-containing apatite film deposited on a Ti plate via an aqueous spray method is described. The mist of the spray solution emitted from a perpendicularly oriented airbrush was made to strike a warmed Ti substrate. The thicknesses of the sprayed film and those heat-treated at 400 °C–700 °C under Ar gas flow were in the range 1.21–1.40 μm. The results of elemental analyses and Fourier transform infrared spectroscopy of the powders that were mechanically collected from the surface of the sprayed film suggest that the film was Ca₁₀(PO₄)6(CO₃) · 2CO₂ · 3H₂O. The presence of the carbonate ion and the lattice CO₂ molecule was confirmed via the aforementioned analyses; the finding was also consistent with the X-ray diffraction patterns of the films and the chemical identity of the sprayed and heat-treated films that were measured using X-ray photoelectron spectroscopy. The sprayed film comprises a characteristic network structure, which contains round particles within the networks, as was observed by field-emission scanning electron microscopy. A scratch test indicated that the shear stress of the sprayed film (21 MPa) significantly improved to 40 and > 133 MPa after heat-treatment at 600 °C and 700 °C, respectively, under Ar gas flow for 10 min.