FT-IR Characterization of the Surface of Aluminum as a Result of Chemical Treatment

Abstract

FT-IR was used to characterize the surfaces of Al after various chemical treatments. All of the oxide surfaces were composed of an anhydrous alumina, aluminum oxyhydroxide (pseudoboehmite) and aluminum hydroxide (close to Gibbsite). The major contaminants in the different oxides are chemisorbed CO₂, carbonates and bi-carbonates. The chromic acid anodized surfaces (CAA) contain more hydroxyls and water than the sulfuric acid anodized surfaces (SAA) while the latter contain more alumina (Al₂O₃). The CAA surfaces have a duplex structure mainly of hydrated and oxyhydroxylated layers over a hydrated alumina layer. The SAA surfaces have a triplex structure composed mainly of hydrated and hydroxylated layers over an oxyhydroxylated layer which is over a hydrated alumina layer. The surfaces chemically converted by the Iridite^© process are composed of a duplex structure of a mixed organic-inorganicl layer over a hydrated alumina. The organic portion of the layer was identified as a carbamate species.

Key Words:

• oxide
• surfaces
• aluminum
• anodized
• alumina
• sectioning
• contaminants.