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首页> 外文会议>International Symposium on State-of-the-Art Application of Surface and Interface Analysis Methods to Environmental Material Interactions: in Honor of James E.Castle's 65th Year, Mar 26-27, 2001, Washington D.C. >CATHODIC REDUCTION OF PASSIVE FILMS ON IRON IN BORATE AND PHOSPHATE BUFFER pH 8.4: DIFFERENT MECHANISMS REVEALED BY IN SITU TECHNIQUES
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CATHODIC REDUCTION OF PASSIVE FILMS ON IRON IN BORATE AND PHOSPHATE BUFFER pH 8.4: DIFFERENT MECHANISMS REVEALED BY IN SITU TECHNIQUES

机译：阴极还原铁中的硼酸根和磷酸盐缓冲液pH 8.4的钝化膜：原位方法揭示了不同的机理

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摘要

The electrochemical behavior of passive Fe and thin, sputter-deposited films of Fe_2O_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 solutions, 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 which is formed in a direct conversion from the Fe oxide passive film. 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.
机译：在硼酸和磷酸盐缓冲液pH 8.4中研究了钝态Fe和溅射沉积的Fe_2O_3薄膜的电化学行为。循环伏安图和原位光吸收测量值（可监控氧化物膜的厚度）表明，在两种pH 8.4溶液中，Fe电极的行为相似，尤其是在低阴极电位下无氧化物的表面。然而，X射线吸收近边缘结构（XANES）研究-可以同时监控样品的平均化合价和厚度的变化-研究表明，在铁上钝化膜还原过程中发生的反应对于这两者是完全不同的电解质。在硼酸盐缓冲液（pH 8.4）中，还原导致钝化膜完全溶解，还原的最终产物是可溶性Fe（2+）。在磷酸盐缓冲液（pH 8.4）中，没有直接步骤溶解到低阴极电位，但是最终的还原产物是金属铁，它是由Fe氧化物钝化膜直接转化形成的。因此，取决于溶液中存在的阴离子的类型，在两种pH 8.4溶液中通过不同的机理在阴极电位形成了无氧化物的裸金属表面。

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