Surface characteristics of titanium anodized in the four different types of electrolyte

This study evaluated the surface characteristics of titanium modified by anodic spark oxidation and a subsequent hydrothermal treatment. The electrolytic compositions of the experimental groups are as follows: GA: 0.015 M dl-α-glycerophosphate disodium salt hydrate (dl-α-GP) and 0.2 M calcium acetate (CA), GB: anodized in 0.015 M β-GP (glycerophosphate disodium salt) and 0.2 M CA, GC: anodized in 0.015 M GP (glycerophosphate disodium salt) and 0.2 M CA, and GD: anodized in 0.015 M GP-Ca (glycerophosphate calcium salt) and 0.2 M CA. Anodic spark oxidation was carried out at 30 mA/cm² to 290 V. In addition, the anodized samples were treated hydrothermally at 300 °C for 2 h in an autoclave system. Regardless of the electrolytic composition, the anodic oxide films on the titanium surface contained pores ∼5 μm in size and the diameter was larger at the protrusion parts than that at the lower parts. The phase of the anodic oxide layer consisted mainly of anatase with a small amount of rutile. HA crystals precipitated on the porous titanium oxide layer after a hydrothermal treatment. Moreover, the morphology of the HA crystals was a dense fine needle shape, which changed according to the electrolytic composition. The mean surface roughness (R_a) was highest in group GB at 0.437 μm. The R_a values of the hydrothermally treated group was approximately 0.14-0.2 μm higher than the anodized groups. Anodic spark oxidation and the hydrothermal treatment resulted in increasing corrosion potential and decreasing corrosion current density, which means an improvement in the corrosion resistance. The surface activity of the specimens in Hanks’ solution was GD > GA > GB > GC.