Improving Bioactivity of Anodic Titanium Oxide (ATO) Layers with Chlorine Ion Addition in Electrolytes

Abstract

Appending diverse quantities of additional elements to the anodizing solution leads to the formation of a highly corrosion-resistant and biocompatible anodic Ti oxide (ATO) on the titanium surface. This study aims to investigate the synergistic effect of chlorine and sulfate ions in the anodizing solution on the formation mechanism and biocompatibility of anodized layers formed on pure Ti. For this purpose, sulfuric acid-based anodizing solutions with different molar ratios () of 0.25, 0.5, and 0.75, and total molars () of 1, 1.5, and 2 M, were utilized for galvanostatic anodizing conditions at different current densities. The response surface methodology was employed on these three anodizing parameters to optimize the quality of anodic Ti oxide layers. Voltage vs. time behavior, SEM surface morphology, and FE-SEM fractured cross-sectional observations were used to thoroughly discuss the formation mechanism. X-ray diffraction method, micro-Raman spectroscopy, and water contact angle measurements were performed to characterize the coatings. Corrosion properties of ATO layers were evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated body fluid (Hanks’ solution). The total molar () is recognized as the most influential factor on the anodic oxide layer properties, and a three-step formation mechanism, based on the competition between the formation and dissolution of anodic Ti oxide, was proposed in detail. The sample anodized with a molar ratio () of 0.5 at a constant current density of 70 mA.cm-2 and a total molar of 1.5 M achieved maximum corrosion resistance with a corrosion current density of 2.138e-11 A.cm-2 compares to 1.39e-8 A.cm-2 for the substrate. Furthermore, the addition of chloride ions to the anodizing bath resulted in more hydrophilic surfaces, promoting the formation of granular hydroxyapatite (HAp) on the TAO coating with maximum corrosion resistance in the Hank solution.