Characterization and structure study of the anodic oxide film on Zircaloy-4 synthesized using NaOH electrolytes at room temperature

Thick crystalline zirconium oxide films were synthesized on Zircaloy-4 substrates by anodic oxidation at room temperature in NaOH solution with a stable applied voltage (300 V). The film is approximately 4.7 mm in thickness. The XPS and SEM analysis shows that the film is a three-layer structure in water, hydroxide and oxide parts. The thickness of that order is 0.01 mm, 1 mm, 3.7 mm, respectively. The oxide layer is composed of tetragonal and monoclinic phases with the volume ratio about 0.2. Furthermore, the thick anodic film acts as a barrier to oxygen and zirconium migrations. It effectively protects zirconium alloys against the worse corrosion. An extremely low passive current density of 0.018 mA/cm2 and a low oxidation weight gain of 0.411 mg/cm2 were also observed in the films