The Characterization of Anodic Aluminas

Abstract

High‐purity aluminum sheet was anodized in eleven different acidic electrolytes: boric, chromic, phosphoric, sulfuric, oxalic, malonic, succinic, tartaric, fumaric, glutaric, and adipic acids. These anodic coatings were analyzed by infrared to determine the composition and nature of each. We found, aside from alumina differences particular to each electrolyte, that the anodic barrier layer can be distinguished from the porous layer by an absorption band in the 1000–900 wavenumber region. Background information for the interpretation of anodic coating infrared data was obtained from the infrared analysis of known mineral forms of alumina. A band correlation table was devised.