Understanding aluminum behaviour in aqueous alkaline solution using coupled techniques: Part II: Acoustic emission study

Abstract 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 4 M 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 4 M 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.

[1]  Digby D. Macdonald,et al.  Evaluation of Alloy Anodes for Aluminum‐Air Batteries II . Delineation of Anodic and Cathodic Partial Reactions , 1988 .

[2]  M. Fregonese,et al.  Initiation and propagation steps in pitting corrosion of austenitic stainless steels: monitoring by acoustic emission , 2001 .

[3]  R. Durand,et al.  Electrochemical behaviour of aluminium in concentrated NaOH solutions , 1999 .

[4]  K. Darowicki,et al.  Comparative Electrochemical Analysis of the Passive Layer Cracking Process on Aluminum Alloys Performed by Means of DC and AC Techniques , 2007 .

[5]  Donald W. Bouldin,et al.  A Cluster Separation Measure , 1979, IEEE Transactions on Pattern Analysis and Machine Intelligence.

[6]  Mickaël Boinet.  Anodisation plasma de métaux (AM60, AI 1050) : suivi par émission acoustique. Structure, composition et propriétés électrochimiques des revêtements obtenus , 2004 .

[7]  V. Macagno,et al.  Electron transfer reaction on passive tantalum electrodes , 1986 .

[8]  M. Urquidi-Macdonald,et al.  Evaluation of alloy anodes for aluminum-air batteries. III: Mechanisms of activation, passivation, and hydrogen evolution , 1988 .

[9]  Anil K. Jain,et al.  Clustering techniques: The user's dilemma , 1976, Pattern Recognit..

[10]  C. Tronel,et al.  An acoustic emission technique for monitoring pitting corrosion of austenitic stainless steels , 1995 .

[11]  A. Despić,et al.  Abnormal yields of hydrogen and the mechanism of its evolution during cathodic polarization of aluminium , 1990 .

[12]  S. Verdier,et al.  Plasma electrolytic oxidation of AM60 magnesium alloy: Monitoring by acoustic emission technique. Electrochemical properties of coatings , 2005 .

[13]  R. Oltra,et al.  Abrasion-corrosion studies of passive stainless steels in acidic media: combination of acoustic emission and electrochemical techniques , 1995 .

[14]  J. Bernard,et al.  Contribution of the Acoustic Emission Technique to Study Aluminum Behavior in Aqueous Alkaline Solution , 2005 .

[15]  S. Verdier,et al.  Formation, structure and composition of anodic films on AM60 magnesium alloy obtained by DC plasma anodising , 2005 .

[16]  Marian Chatenet,et al.  Understanding aluminum behaviour in aqueous alkaline solution using coupled techniques. Part I. Rotating ring-disk study , 2006 .

[17]  M. Seo,et al.  The cathodic polarization of aluminum covered with anodic oxide films in a neutral borate solution—II. Film breakdown and pit formation , 1994 .

[18]  M. Seo,et al.  The cathodic polarization of aluminum covered with anodic oxide films in a neutral borate solution—I. The mechanism of rectification , 1994 .

[19]  A. Arora.  Acoustic emission characterization of corrosion reactions in aluminum alloys , 1984 .

[20]  A. W. Hassel,et al.  Initial Stages of Cathodic Breakdown of Thin Anodic Aluminium Oxide Films , 1995 .

[21]  H. Idrissi,et al.  Use of acoustic emission technique for the early detection of aluminum alloys exfoliation corrosion , 2002 .

[22]  L. Roué,et al.  In-situ study of the cracking of metal hydride electrodes by acoustic emission technique , 2008 .

[23]  H. Inoue,et al.  In Situ Monitoring of Hydrogen Storage Alloy Negative Electrode during Charging by an Acoustic Emission Technique , 2006 .