Effect of Fluoride or Chloride Ions on the Morphology of ZrO2 Thin Film Grown in Ethylene Glycol Electrolyte by Anodization

0.3 wt % ammonium fluoride (NH4F) or ammonium chloride (NH4Cl) was added to ethylene glycol (EG) as an active ingredient for the formation of anodic oxide comprising of ZrO2 nanotubes (ZNTs) by anodic oxidation of zirconium (Zr) at 20 V for 10 min. It was observed that nanotubes were successfully grown in EG/NH4F/H2O with aspect ratio of 144.3. Shorter tubes were formed in EG/NH4F/H2O2. This could be due to higher excessive chemical etching at the tip of the tubes. When fluoride was replaced by chloride in both electrolytes, multilayered oxide resembling pyramids was observed. The pyramids have width at the bottom of 3-4 μm and the top is 1-2 μm with 10.7 μm height. Oxidation of Zr in EG/NH4Cl/H2O2 was rater rapid. The multilayered structure is thought to have formed due to the re-deposition of ZrO2 or hydrated ZrO2 on the foil inside pores formed within the oxide layer. XRD result revealed an amorphous structure for as-anodized samples regardless of the electrolytes used for this work.