Etching titanium with 70 % H2SO4: Effects on morphology, composition, and corrosion resistance of anodic films

Efficient surface preparation is crucial for enhancing the corrosion resistance of titanium before anodizing. This study explores the use of concentrated sulfuric acid (70 % H₂SO₄) for titanium surface preparation under various temperatures (20 °C and 50 °C) and immersion times (15 and 30 min). Surface modifications in morphology and composition are analyzed using SEM, GDOES, XRD, and XPS techniques. Mild etching conditions (low temperatures and short durations) have been proven to be insufficient for removing surface contaminants, such as titanium carbide. On the contrary, harsher conditions (extended immersion times or/and higher temperatures) effectively eliminate impurities but result in hydrogenation of the titanium surface. In this case, a titanium hydride layer (TiH₂) appears on the surface, modifying its morphology and roughness. On this occasion, the combination of XRD and GDOES techniques proves to be effective in revealing the presence of hydrides. Moreover, hydrogenation significantly increases with immersion time and temperature. Eventually, the impact of etching conditions on anodic film corrosion properties is also evaluated by EIS measurements. The study highlights that performances of anodic films are strongly influenced by the etching parameters. Indeed, titanium hydride layers can adversely affect corrosion resistance of anodic films. Therefore, to ensure optimal results, etching conditions must strike a balance between thorough cleaning and minimizing hydrogenation, thereby preserving the corrosion resistance of anodic films.