Corrosion rates and negative difference effects for Al and some Al alloys
Corrosion rates and negative difference effects for Al and some Al alloys
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DOI：
10.1023/a:1003447018115
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发表时间：
1999-01-01
影响因子：
2.9
通讯作者：
Popic, JP
中科院分区：
文献类型：
--
作者：
Drazic, DM;Popic, JP
采用铂环旋转盘环技术定量检测铝盘电极在开路电位下自腐蚀或阳极极化过程中的析氢量，研究了阳极电流增加时析氢量异常增加的现象（负差效应）。用高纯度Al（99.999%）、工业级Al（99.5%）（Al-T）和Al-In合金（0.074%In）在脱气的0.5M NaCl水溶液（pH类似于6.5）和用HCl酸化至pH值为3.0、2.0和1.0的NaCl溶液中进行实验。结果表明，在中性溶液中，所有三种材料的腐蚀速率由水分子解离速率控制，或在更酸性的溶液中，由组合的水分子解离速率和H+离子放电速率控制。在3-10 μ A·cm ~（2）范围内，99.999%Al的腐蚀速率最低。Al-T和Al-In中的杂质以相似的方式增加阴极极化下的析氢速率，但对负差效应的影响非常不同。高纯Al和Al-T具有相似的负差效应（8-15%），而In的存在将其降低到仅约1%。在比E-pit更负的电位下，没有观察到点蚀和负差效应。因此，负差异效应与阳极点蚀溶解机制有关。这个问题的几个方面进行了更详细的讨论。
The rotating disc-ring technique with a Pt ring was used to quantitatively detect hydrogen evolved on an Al-disc electrode during spontaneous corrosion at open-circuit potential or during anodic polarization of an Al disc to study the unusual increase of H-2 evolution with increase in anodic current (the so called negative difference effect). Experiments were made with high purity Al (99.999%), technical grade Al (99.5%) (Al-T) and Al-In alloy (0.074% In) in deaerated 0.5 M aqueous NaCl solution (pH similar to 6.5) and NaCl solutions acidified with HCl to pH values of 3.0, 2.0 and 1.0. It was shown, in neutral solutions, that the corrosion rates of all three materials are controlled by the rate of water molecule dissociation or in more acid solutions, by the combined water molecule dissociation rate and H+ ion discharge rate. The corrosion rates of all three materials in the range of 3-10 mu A cm(2) was the lowest for 99.999% Al. The impurities in Al-T and Al-In increase the hydrogen evolution rate at cathodic polarizations in a similar manner, but very differently affect the negative difference effect. High purity Al and Al-T have a similar negative difference effect (8-15%), while the presence of In decreases it to only about 1%. No pitting and no negative difference effect were observed at potentials more negative than E-pit. Therefore, the negative difference effect is connected with the anodic pitting dissolution mechanism. Several aspects of this problem are discussed in more detail.