Inhibition of Aluminum Alloy 2024 Corrosion by Vanadates: An In Situ Atomic Force Microscopy Scratching Investigation

100

111

Nuclear magnetic resonance ͑NMR͒ measurements were made on aqueous vanadate solutions to characterize speciation as a function of pH and vanadate concentration. Additionally, potentiodynamic polarization measurements were carried out on Al alloy 2024-T3 in 50 mM NaCl solutions in which pH and vanadate concentration were systematically varied. Results showed that inhibition by vanadates occurred mainly in alkaline solutions where tetrahedrally coordinated vanadates, metavanadate and pyrovanadate, were abundant. Inhibition was not observed in solutions where octahedrally coordinated decavanadates predominated. Anodic inhibition, in the form of increased pitting potential, was observed in both aerated and deaerated solutions. In contrast, cathodic inhibition was observed only in aerated solutions acting primarily through the suppression of oxygen reduction. Energydispersive spectroscopy, used to collect chemical maps from aluminum coupons exposed to vanadate solutions, showed the suppression of Al 2 CuMg particle dissolution compared to vanadate-free solutions. NMR measurements were also used to track changes in vanadate speciation with time, pH adjustment, and with exposure to metallic aluminum surfaces. NMR showed noninhibiting octahedrally coordinated decavanadates rapidly decompose into inhibiting tetrahedrally coordinated metavanadates and pyrovanadates after alkaline pH adjustment. While decomposition begins immediately upon pH adjustment, equilibrium may not be reached even after significant time periods.

Section: Discussionmentioning

confidence: 99%

Corrosion Inhibition of Aluminum Alloy 2024-T3 by Aqueous Vanadium Species

Ralston

Chrisanti

Young

et al. 2008

100

111

“…[5][6][7] Additionally, significant efforts over the last decade have been devoted to understanding corrosion inhibition of AA2024-T3 by vanadates. [8][9][10][11][12] For AA2024-T3, inhibition has been reported to be pH and concentration dependent (speciation dependent) and has been strongly linked to tetrahedrally coordinated vanadates reducing cathodic oxygen reduction kinetics on Cu-containing intermetallic compounds (IMCs) through a surface adsorption mechanism. [11][12][13][14] Other works have shown that vanadates also provide inhibition to Zn-rich Al alloys such as AA7075.…”

mentioning

confidence: 99%

Corrosion Inhibition of Zinc by Aqueous Vanadate Species

Hurley

Ralston

Buchheit

2014

This study presents a characterization of the degree and mechanism of corrosion inhibition of Zn by vanadate inhibitors. A combination of open circuit potential measurements, anodic and cathodic polarization, and Raman spectroscopy were used to compare corrosion inhibition of Zn exposed to or pre-treated with a dilute ∼pH 6.3 NaVO 3 +NaCl solution, which likely contained predominantly tetrahedrally coordinated vanadate species, relative to controls. The presence of vanadate caused a decrease in corrosion current density of up to two orders of magnitude due to overall mixed anodic and cathodic inhibition associated with the formation and/or stabilization of adherent surface films. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0381410jes] All rights reserved. Vanadates have been shown to be corrosion inhibitors on a range of alloys including Mg, 1,2 Fe, 3,4 and Zn. 5-7 Additionally, significant efforts over the last decade have been devoted to understanding corrosion inhibition of AA2024-T3 by vanadates. [8][9][10][11][12] For AA2024-T3, inhibition has been reported to be pH and concentration dependent (speciation dependent) and has been strongly linked to tetrahedrally coordinated vanadates reducing cathodic oxygen reduction kinetics on Cu-containing intermetallic compounds (IMCs) through a surface adsorption mechanism.11-14 Other works have shown that vanadates also provide inhibition to Zn-rich Al alloys such as AA7075. 15,16 This, in combination with evidence of vanadate inhibition on Zn-based materials, 5-7 has led to speculation that vanadates likely interact with the Zn-rich phases in 7xxx series Al alloys (possibly in addition to the Cu-rich features). Zn-rich IMCs in 7xxx series Al are relatively active to the surrounding matrix 17 and generally not associated with oxygen reduction (as compared to generally noble Cu-containing IMCs in Al alloys). It has been reported that the primary cathodic reaction at a Zn surface in water is hydrogen evolution through the reduction of water, followed secondarily by the reduction of dissolved molecular oxygen. 18 However, a number of works have indicated that in dilute chloride electrolytes with available oxygen, the oxygen reduction reaction is the dominant cathodic reaction on Zn. 19 This raises a critical question: if vanadates act as corrosion inhibitors on Zn (or interact with Zn-rich features in Al alloys) what is the mechanism of inhibition? Given that both oxygen reduction and water reduction are available cathodic reactions on Zn and that Zn-rich IMCs in Al alloys generally do not support oxygen reduction this may suggest diff...

“…16 Frankel et al found that vanadate provided very effective corrosion inhibition on S phase particles even when the protective layer was disturbed with AFM scratching. 22 The FIB data provide additional insight into vanadate interactions with IMCs. Although the FIB image in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…In particular, vanadate has shown good inhibition on aluminum alloys in the form of soluble vanadate, [17][18][19][20][21][22][23][24][25][26] vanadate-based coatings, 27-29 and ion exchange compounds pigment for primers. 30 Iannuzzi et al used polarization and split cell experiments to show that vanadate acted as a cathodic inhibitor on AA2024 by suppressing the oxygen reduction reaction (ORR) by a physically adsorbed vanadate monolayer.…”

mentioning

confidence: 99%

“…15 Previous work examining vanadate as a corrosion inhibitor on aluminum alloys was undertaken under ambient temperatures. 17,18,[20][21][22]24,25,27,28,31 Being a thermally activated process, the kinetics of corrosion reactions are expected to be accelerated at elevated temperatures. 34,35 In particular, temperature will affect the galvanic coupling between active and cathodic sites on the alloy's surface.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Inhibition Performance Study of Vanadate on AA2024-T3 at High Temperature by SEM, FIB, Raman and XPS

Hurley

Buchheit

2015

The inhibition of AA2024-T3 by vanadate at temperatures ranging from 10 • to 80 • C was studied using various characterization techniques. SEM showed that in the presence of vanadate, no corrosion was observed on any intermetallic particles, including the reactive Al 2 CuMg (S phase) at temperatures up to 50 • C. Although trenching occurred around the S phase particles when solution temperature increased to 70 • C and above, S phase was protected by vanadate-bearing film. Raman spectroscopy showed a peak indicating polymeric vanadate, which increased in intensity with increasing temperature with the highest intensity at 80 • C. The high vanadium concentration at 80 • C was attributed to fast reduction reaction kinetics of vanadate by Al or Mg. This reduction reaction is confirmed by XPS, and the reduced forms of vanadium appeared to promote vanadate (V 5+ ) polymerization leading to the formation of vanadate films. Additionally, elevated temperatures appeared to increase vanadate polymerization kinetics. This reductive adsorbed vanadate film also enabled the samples treated in vanadate at higher temperature to have residual inhibition in NaCl without inhibitors. The reduced forms of vanadium were found to be easily oxidized under ambient aerated solution conditions. Exposure of treated samples in air further increased the corrosion resistance. AA2024-T3 (Al-4.4Cu-2.5Mg-0.6Mn) is a high strength Al alloy that is susceptible to many forms of localized corrosion due to its heterogeneous microstructure.1,2 Localized corrosion is focused at secondary phase intermetallic compounds (IMCs).3,4 Two common IMCs of interest in AA2024 are S-phase (Al 2 CuMg) and AlCuFeMn(Si) particles. These two IMC types account for the majority of particles found in AA2024, both in number and surface area.4,5 AlCuFeMn(Si) particles generally act as cathodes to the matrix, and corrosion occurs as trenching around the particles under corrosive conditions. 3,6-10 S-phase particles are initially active and dissolve by dealloying.4 However, upon the dissolution of Mg and Al from these particles, they become Cu-rich and thereafter act as a local cathode. 4,6,[11][12][13] In view of recent advances in understanding the chemistry of vanadate, it has become an intriguing inhibitor to the research community.14-20 Vanadate has proven to be a promising candidate to replace toxic chromate as a corrosion inhibitor. In particular, vanadate has shown good inhibition on aluminum alloys in the form of soluble vanadate, [17][18][19][20][21][22][23][24][25][26] vanadate-based coatings, 27-29 and ion exchange compounds pigment for primers. 30 Iannuzzi et al. used polarization and split cell experiments to show that vanadate acted as a cathodic inhibitor on AA2024 by suppressing the oxygen reduction reaction (ORR) by a physically adsorbed vanadate monolayer. 23,24 The inhibition of vanadate on AA2024-T3 was also reported by Ralston et al. while studying corrosion inhibition imparted by vanadate on IMCs found in AA2024 and AA7075-T6. 25,31The effect of temperat...