Abstract
The incorporation of sulphate into anodic coatings formed in H2SO4 and CrO2-H2SO4 electrolytes has been studied using S35 as tracer in the sulphuric acid. This has shown that sulphate is included in the anodic coating as part of the anodic process. During the formation of the barrier layer the sulphate content fluctuates but once the barrier layer is established these fluctuations cease. During the growth of the main porous superstructure, the percentage of sulphate in the film decreases slightly but progressively with increasing anodizing time. Sulphate ions are more readily incorporated into anodic coatings than are oxalate ions. The reasons for these phenomena are discussed in relation to the current views on the mechanism of anodic coating formation.

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