Adsorption of sulfate and chloride ions on aluminum

228

122

Metals and alloys such as aluminum (Al), stainless steels, and nickel-based alloys exhibit corrosion resistance in a wide range of environments due to the presence of protective, passive oxides. However, in environments that contain aggressive anions such as chloride, Cl − , the passive film becomes unstable and degrades locally causing film breakdown and pitting corrosion. A number of theories describing the initiation of pitting corrosion have been postulated and discussed but to date there is no consensus on the mechanism of breakdown. Since all current mechanisms require Cl − interactions for oxide film breakdown in Cl − containing environments, the question is what is the nature of the interaction of aggressive anions such as Cl − with the passive film, adsorption and/or absorption, leading to pitting? This communication focuses on the interaction of Cl − with the passive oxide film on pure aluminum by reviewing and summarizing the available experimental data concerning Cl − interactions. It should also be noted that the observations for Cl − interactions with Al reviewed and summarized herein might not be applicable to all metals and alloys. Technologically important metals and alloys such as aluminum (Al), stainless steels, and nickel-based alloys exhibit corrosion resistance in a wide range of environments due to the presence of protective, passive oxides.1-90 The passive oxides behave as kinetic barriers, which inhibit further oxidation of the underlying thermodynamically reactive metals. However, in environments that contain aggressive anions such as chloride, Cl − , the passive film becomes unstable and degrades locally causing film breakdown and localized corrosion, which in turn decreases the service life of the materials. The consequence of discrete oxide failure is localized corrosion, which occurs in the forms of crevice corrosion in occluded sites and metastable or stable pitting corrosion on open surfaces. It is generally agreed that localized corrosion occurs in two distinct steps: initiation and propagation.A number of theories describing the initiation of pitting corrosion have been postulated and discussed.

Section: Interactions At the Oxide/solution Interfacementioning

confidence: 97%

“…pH dependence of chloride adsorption on aluminum ( R is the surface concentration of the radioactive isotope) in 0.1 M NaClO 4 . 78 Reproduced by permission of Elsevier Limited.…”

Section: Oxide Thicknessmentioning

confidence: 99%

Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

Natishan

O’Grady

2014

228

122

“…[3][4][5][6][7][8][9][10][11] After all, localized corrosion can only occur if an otherwise protective passive film is present and undergoes a breakdown event. Studies have focused on linking film breakdown events to the composition and structure of the passive film using techniques such as X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM).…”

Section: Current Statusmentioning

confidence: 99%

Perspective—Localized Corrosion: Passive Film Breakdown vs Pit Growth Stability

Frankel

Scully

2017

177

107

A debate about the critical step in localized corrosion has raged for decades. Some researchers focus on the composition and structure of the passive film associated with the initial breakdown of the film, whereas others consider that the susceptibility to pitting is controlled by the pit growth kinetics and the stabilization of pit growth. The basis for a unified theory of pitting is presented here in which pit stability considerations are controlling under aggressive conditions (harsh electrolytes and extreme environments and/or susceptible microstructures) and the passive film properties and protectiveness are the critical factors in less extreme environments and/or for less susceptible alloys.

“…The initial decrease in the intensity of the transmitted light directly indicated that the ingressing electrolyte reacted with the metal (Al) giving rise to a light-absorbing corrosion product. It appeared that NaCl may have reacted 41 as well as incorporated 13,[42][43][44][45] with/into the native oxide to form dissolved interfacial oxy-chloro compounds and/or a defect-rich and possibly semiconducting metal oxide phase. As such, both the initial decrease of light intensity, and the slight negative mirror shift (see Fig.…”

Section: Resultsmentioning

confidence: 99%

Real-Time Monitoring of Aluminum Crevice Corrosion and Its Inhibition by Vanadates with Multiple Beam Interferometry in a Surface Forces Apparatus

Shrestha

Baimpos

et al. 2015

Crevice corrosion (CC) of metals remains a serious concern for structural materials. Yet a real-time in situ visualization of corrosion, and its inhibition within a confined geometry, remains challenging. Here, we present how multiple-beam interferometry in a Surface Forces Apparatus can be utilized to directly visualize corrosion processes in real-time and with Ångstrom resolution within welldefined confinement geometries. We use atomically smooth muscovite mica surfaces to form round-shaped ∼1000 μm 2 crevices on aluminum. After exposure to NaCl solutions we can detect and track active sites of aluminum corrosion within this confined geometry. CC of aluminum randomly initiates in the confined crevice mouth, where the distance between apposing surfaces is between 20-300 nm. We can directly track oxide dissolution/formation, and corrosion-rates as well as their retardation due to sodium vanadate inhibitors present in solution. Formation of a compacted oxide layer effectively inhibits CC in 5 mM NaCl solutions with 2.5 mM of added NaVO 3 , while inhibition rapidly breaks down at chloride concentrations above 50 mM. Breakdown of the inhibition-layers is initiated by rapid dissolution of the protective oxide within the confined zone. Our technique may be adapted for monitoring CC, corrosion inside of crack-tips, and evaluation of inhibitor efficiencies in a variety of metals.