Fabrication of thick gel-like films by anodizing iron in a novel electrolyte based on dimethyl sulfoxide and H2SiF6

The thick bi-layered gel-like film has been grown by anodizing iron in a novel electrolyte composition based on dimethyl sulfoxide and silica hexafluoride acid (H2SiF6) and examined. The thickness of the anodic film composed of the inner orange-colored nanoporous layer and the outer cherry-colored gel-like layer increased at a constant rate up to 40–50 μm depending on the bath composition and anodizing conditions. Under drying and subsequently annealing, the gel layer shrinks and cracks producing hierarchical morphology of thick films mainly composed of hematite (a-Fe2O3). Scanning electron microscopy, Mössbauer, Raman and energy dispersive X-ray spectroscopies, and X-ray diffraction have been applied to reveal the composition and morphology of these novel films before and following various post-treatments.

► The thick nanoporous bi-layered film formation by iron anodizing is presented. ► A novel electrolyte is based on dimethyl sulfoxide and silica hexafluoride acid. ► On drying and subsequently annealing a hematite (a-Fe2O3) possessing a hierarchical morphology is formed.