An electron-yield EXAFS study of anodic-oxide and hydrated-oxide films on pure aluminium

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Abstract
The molecular structures of the amorphous films formed on pure aluminium by anodic oxidation in sodium tartrate and phosphoric acid electrolytes, which are known to give quite different oxide morphologies, have been investigated using the technique of electron-yield EXAFS. The Al-0 ‘bond length’ derived from the EXAFS is found to be different for these two types of film, which suggests different states of aluminium-oxygen coordination. The two types of film also show quite different behaviour when immersed in hot water. The tartrate-formed oxide shows only slight morphological change and a correspondingly small change in Al—O bond length, whereas the phosphoric acid-formed film undergoes an extensive change of morphology and bond length. These results are discussed in relation to the structural chemistry of the hydration process.