Cathodic reduction of passive films on iron in borate and phosphate buffer ph 8.4: different mechanisms revealed by in situ techniques.

Schmuki, P. ; Virtanen, S. ; Isaacs, H. S.

Technical Information Center Oak Ridge Tennessee

关键词: Borates;    Phosphates;    Passivation;    Buffers;    Dissolution;   

RP-ID  :  DE2001782048

学科分类：工程和技术（综合）

美国|英语

来源: National Technical Reports Library

【 摘 要 】

The electrochemical behavior of passive Fe and thin, sputter-deposited films of Fe(sub 2)O(sub 3) was studied in borate and phosphate buffer pH 8.4 solutions. Cyclic voltammograms and in situ light absorption measurements--which enable the monitoring of the oxide film thickness--indicate a similar behavior of the Fe electrode in both pH 8.4 solution, especially a presence of a oxide-free surface at low cathodic potentials. However, X-ray absorption near edge structure (XANES) studies--which allow a simultaneous monitoring of changes in the samples' average valency and thickness--reveal that the reactions taking place during reduction of the passive film on iron are completely different for the two electrolytes. In borate buffer (pH 8.4), reduction leads to a complete dissolution of the passive film and the end product of reduction is soluble Fe(2+). In phosphate buffer (pH 8.4), there is no dissolution in a direct step to low cathodic potentials, but the resulting reduction product is metallic iron. Hence, the formation of the bare oxide-free metal surface at cathodic potentials takes place by different mechanisms in the two pH 8.4 solutions, depending on the type of anion present in the solution.