Fabrication and Characterization of Anodic Films onto the Type-304 Stainless Steel in Glycerol Electrolyte

Porous films without periodic structuration were formed by direct current anodizing the surface of type-304 stainless steel in glycerol solution containing NH 4 F and H 2 O at elevated temperatures. Formed in the solutions containing both NH 4 F and H 2 O at the constant voltage mode of up to 50 V, these films are thin (∼1.0–1.2 μm) and yellow, whereas those formed at higher voltages, ca. 60–70 V, are thicker (up to 15 μm) and greenish. Note that these porous films are composed of both amorphous and crystalline species. X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and X-ray photoemission spectroscopy (XPS) investigations and the detailed chemical analysis of incorporated elements revealed the complex nature of these films varied depending on the anodizing solution composition and voltage value applied. On the basis of the obtained data, the possible mechanism of formation of the glycerol anodic films on the SS304 substrate is presented. Compositional and structural transitions of as-grown films to material composed of crystalline Cr 1.3 Fe 0.7 O 3 and spinel-type species were achieved via calcination procedure of anodized samples in air at 700 °C.