Understanding aluminum behaviour in aqueous alkaline solution using coupled techniques: Part II: Acoustic emission study
Understanding aluminum behaviour in aqueous alkaline solution using coupled techniques: Part II: Acoustic emission study
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DOI：
10.1016/j.electacta.2009.06.038
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发表时间：
2010-04
影响因子：
6.6
通讯作者：
M. Boinet;Julien Bernard;M. Chatenet;F. Dalard;S. Maximovitch
中科院分区：
文献类型：
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作者：
M. Boinet;Julien Bernard;M. Chatenet;F. Dalard;S. Maximovitch
本工作的重点是纯铝在碱性介质中的行为，通过耦合声发射（AE）和直接氢伏安法的电化学。我们特别监测，记录和分析的声发射活动所产生的铝电极作为其极化的函数在纯铝在4 M氢氧化钾水溶液中的线性扫描伏安法（从阳极到阴极电位）。电化学和声发射的这种原位耦合显示了两种信号之间的完美相关性。在使用统计处理对AE信号进行仔细分析之后，并且基于五个相关AE参数（上升时间、持续时间、振幅、绝对能量、最大频率），我们可以分离在铝电极处发生的AE信号的各组。我们进一步将它们与不同的（可能伴随的）电化学现象联系起来，这些电化学现象在强碱性介质中铝电极极化时发生。首先，我们证实了在4 M氢氧化钾溶液中，对于铝开路电位为正的电位，析氢开始;这种小但不可忽略的氢产生与铝氧化平行发生。第二，氧化铝仅存在于开路电位附近;而对于高铝氧化电位，它们被侵蚀，而在高析氢电位下，它们被剥落。后者的过程可能是加速析氢诱导的电解质的碱化。第三，记录了两种析氢模式：一种在氧化物上，另一种在裸铝上，后者是最有效的。这种在极低电极电位下的强析氢可能有助于去除铝上存在的脆性残余氧化物/钝化膜（我们将其称为氢辅助铝剥落腐蚀），因此导致铝电极的快速腐蚀。因此，铝在强碱性介质中从不处于免疫状态。
This work focuses on the behaviour of pure aluminum in alkaline media, by coupling both acoustic emission (AE) and direct hydrogen voltammetry to electrochemistry. We notably monitored, recorded and analyzed the acoustic emission activity generated by the aluminum electrode as a function of its polarization during a linear sweep voltammetry (from anodic to cathodic potentials) on pure aluminum in 4M aqueous potassium hydroxide solution. Such in situ coupling of electrochemistry and acoustic emission shows a perfect correlation between the two signals. After careful analysis of the AE signal using a statistical treatment, and based on five relevant AE parameters (rise time, duration, amplitude, absolute energy, maximum frequency), we could separate various groups of AE signals occurring at the aluminum electrode. We further linked them to the different (and possibly concomitant) electrochemical phenomena, which are taking place upon polarization of the aluminum electrode in strong alkaline medium. First, we confirmed that hydrogen evolution initiates for potentials positive to aluminum open circuit potential in 4M potassium hydroxide solution; such small but non-negligible hydrogen production occurs in parallel to aluminum oxidation. Second, aluminum oxides are present only around the open circuit potential; whereas they are eroded for high aluminum oxidation potentials, they are flaked off at high hydrogen evolution potentials. Such latter process is probably accelerated by the hydrogen evolution-induced alkalization of the electrolyte. Third, two modes of hydrogen evolution are recorded: one on the oxide, the other one on bare aluminum, the latter being the most efficient. This strong hydrogen evolution at very low electrode potential probably assists the removal of the brittle residual oxide/passive film present on aluminum (which we denote as hydrogen-assisted aluminum exfoliation corrosion), therefore causing the rapid erosion of the aluminum electrode. As a result, aluminum is never in immunity conditions in strong alkaline medium.