Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
DFT calculations of initial localized corrosion of aluminum: Influence of aqueous ad-layer, chloride ions, and intermetallic particles
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Localized corrosion of aluminum (Al, here including Al alloys) involves a series of physico-chemical processes at the interface between the metal and the aqueous ad-layer or the aqueous solution. The mechanisms that govern localized corrosion are quite complex and have been the subject of many experimental studies. Efforts to improve our understanding through computational studies have so far been much more limited. The primary aim of this Doctoral Thesis was to apply Density Functional Theory (DFT), together with some Molecular Dynamics calculations (limited effort), to gain a deeper mechanistic understanding of some of the most influential factors for the initiation of localized corrosion of Al: chloride ions, intermetallic particles (IMPs) and the presence of an aqueous ad-layer on the solid phase.In the scientific literature three scenarios have been proposed for the interaction of chloride ions with an aluminum and/or passive aluminum surface: through adsorption onto the passive layer, through breakdown of the same layer or through migration of chloride ions into the layer. DFT-calculations have been able to explore these scenarios in more detail, and provide evidence that chloride ions induce partial de-passivation in several ways. On the bare Al surface, chloride ions may inhibit the re-passivation through competitive adsorption with oxygen molecules, as suggested by density of state calculations. Chloride ions are also found to migrate via oxygen vacancies into the inner part of the investigated aluminum oxide films (α- and γ-Al2O3), where a critical amount of accumulated chloride can promote meta-stable pitting propagation. γ-Al2O3 exhibits a more open structure than α-Al2O3, resulting in a lower energy barrier for chloride migration.Micro-galvanic effects induced by Volta potential differences between representative intermetallic particles (Mg2Si and Al2Cu) and the surrounding Al matrix were predicted by calculating the work function of the bare surfaces of these phases with DFT. These values vary with crystalline face orientation and with terminal atomic configuration in the outmost surface layer. Calculated Volta potential differences between IMPs and Al show a reasonable agreement with reported experimental data, and suggest the possibility of predicting the nobility of specific IMPs relative to Al. Moreover, both DFT and scanning Kelvin probe force microscopy show evidence of electrochemical nobility inversion of Mg2Si versus Al upon adsorption of pure water ad-layers. This implies that an originally- 2 -cathodic Mg2Si phase becomes anodic compared to Al upon water adsorption, and is attributed to surface relaxation according to DFT calculations. With subsequent introduction of chloride ions into the water ad-layer, the nobility inversion of both Mg2Si and Al2Cu retains. This is due to a strong oxidizing effect of water on Al, while the effect of chloride seems less pronounced.In all, these and other examples presented show that DFT-calculations can provide more detailed atomistic and molecular information on physico-chemical processes governing localized corrosion of Al than experiments alone can do.

Abstract [sv]

Kvantmekaniska metoder såsom täthetsfunktional-teori (Eng. Density functional theory, DFT) har under de senaste årtiondena börjat tillämpas på allt mer komplicerade modellsystem. I denna doktorsavhandling har det primära syftet varit att tillämpa DFT för att kunna uppnå en djupare förståelse för mekanismerna bakom initiering av lokala korrosionsangrepp på aluminium. I möjligaste mån har de teoretiskt framtagna resultaten även jämförts med experimentella data. Lokalkorrosion är en komplicerad fysikalisk-kemisk process och en utmaning har varit att definiera frågeställningen så att förenklade men ändå relevanta modellsystem går att beräkna med DFT. Tre faktorer, som alla har stor betydelse för den lokala korrosionsinitieringen, har studerats mer ingående: kloridjoners inverkan, mikrogalvaniska effekter orsakade av intermetalliska sekundärfaser i aluminium-matrisen, och närvaron av en tunn adsorberad vattenfilm. 

Baserat på tidigare experimentella studier finns tre möjliga sätt på vilka kloridjoner kan påverka initieringen av lokalkorrosion: genom adsorption på aluminiumets passivfilm, genom strukturell nedbrytning av passivfilmen eller genom migration av kloridjoner genom passivfilmen. DFT-beräkningarna har kunnat belysa dessa processer mer ingående. Adsorberat klorid kan deformera ett monolager adsorberat syre, som täcker den rena aluminiumytan, och därvid åstadkomma en minskad strukturell stabilitet och passiverande förmåga hos monolagret syre. Bindningen mellan aluminium- och syreatomer är mycket stark och klorid kan inte bryta upp den bindningen. Däremot kan adsorberat klorid hämma repassiveringsförmågan hos monolagret syre genom att konkurrera med syre om möjliga adsorptionsplatser på aluminiumytan. DFT-beräkningarna visar även att kloridtransport sker via syrevakanser i den undersöka aluminiumoxidfilmen (α-Al2O3), som uppvisar en relativt liten energibarriär för klorid-migration. Energibarriären minskar ytterligare genom dopning med andra legeringselement eller genom klorid som redan placerats i oxidgittret. Transport av klorid genom aluminiumoxiden försämrar dess skyddande egenskaper. Det sker genom att oxidstrukturen relaxerar men också genom en kraftig sänkning av oxidens utträdesarbete (eng. Work function). När tillräckligt med klorid, i form av reaktionsintermediärer, samlats i fasgränsen mellan oxid och aluminium uppstår förutsättningar för en stabil tillväxt av det lokala korrosionsangreppet. Jämfört med α-Al2O3 uppvisar en annan tänkbar oxidfas, γ-Al2O3, en mer öppen struktur och lägre energibarriär, vilket underlättar kloridtransporten genom γ-Al2O3.

Mikrogalvaniska effekter mellan två representativa intermetalliska sekundärfaser (Mg2Si respektive Al2Cu) och den omkringliggande aluminium-matrisen har kunnat uppskattas genom uträkningar av skillnaden i Volta-potential mellan de intilliggande faserna. De beräknade värdena på Volta-potential korrelerar utmärkt med motsvarande uppmätta värden för såväl rena som vattenadsorberade ytor. Potentialskillnaderna visar sig vara beroende av de ingående fasernas orientering, av strukturen hos den allra yttersta ytans atomära konfiguration, samt av adsorption av olika species såsom klorid eller vatten. På en ren aluminiumyta kommer adsorberade species med högt utträdesarbete att resultera i en höjning av systemets totala utträdesarbete, och tvärt om. Beräkningarna visar att adsorberat vatten har en starkt oxiderande effekt på aluminium, oavsett närvaron av klorid. I överensstämmelse med experiment kan de undersökta systemen genomgå så kallad elektrokemisk inversion. Det innebär att en intermetallisk sekundärfas, som från början var katodisk relativt aluminiummatrisen, blir anodisk när mängden adsorberat vatten på ytan ökar. Fenomenet tillskrivs förändringar i atomär ytkonfiguration hos de ingående faserna i samband med adsorption. 

Sammantaget visar dessa och andra exempel i avhandlingen hur DFT-beräkningar av fysikaliskt-kemiska förutsättningar under initiering av lokalkorrosion på aluminium kan leda till mer detaljerad molekylär information än vad som vore möjligt med enbart experimentella studier.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. , p. 59
Series
TRITA-CBH-FOU ; 2019:66
Keywords [en]
aluminum alloys, alumina, chloride, surface adsorption, aqueous ad-layer, localized corrosion, corrosion initiation, work function, micro-galvanic effect, density-functional theory, Volta potential, scanning kelvin probe force microscopy
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-264028ISBN: 978-91-7873-372-9 (print)OAI: oai:DiVA.org:kth-264028DiVA, id: diva2:1372029
Public defence
2019-12-13, Lecture Hall K1, Teknikringen 56, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 2019-11-21

Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-11-21Bibliographically approved
List of papers
1. First-Principle Calculation of Volta Potential of Intermetallic Particles in Aluminum Alloys and Practical Implications
Open this publication in new window or tab >>First-Principle Calculation of Volta Potential of Intermetallic Particles in Aluminum Alloys and Practical Implications
Show others...
2017 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 164, no 9, p. C465-C473Article in journal (Refereed) Published
Abstract [en]

This work presents a theoretical assessment of galvanic (relative) nobility of four intermetallic particles (IMPs), Al2Cu, Al2CuMg, Mg2Si andMgZn(2), in aluminum alloys through work function calculation based on density functional theory (DFT). The concepts of work function, Volta potential and relative nobility are discussed with respect to the IMPs and aluminum matrix. The calculated Volta potentials are compared with reported experimental Volta potentials measured by scanning Kelvin probe forcemicroscopy (SKPFM). Various crystal faces and terminal types are examined in the DFT calculation, showing that these two factors have a significant effect on the work function value. Considering the large divergence in the reported experimental data, the comparison shows a general agreement between the calculated and experimental Volta potential data for the investigated IMPs. The DFT calculations provide theoretical explanations for several experimental phenomena. The results demonstrate that DFT calculation is a valuable theoretical approach for assessment of the relative nobility of different phases in the alloys, providing complementary information to experimental data from SKFPM. Moreover, the implications of the calculated Volta potentials are discussed with respect to the corrosion potentials.

Place, publisher, year, edition, pages
Electrochemical Society, 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-264031 (URN)10.1149/2.0191709jes (DOI)000413256400059 ()2-s2.0-85039868792 (Scopus ID)
Note

QC 20191122

Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-11-22Bibliographically approved
2. Volta Potential Evolution of Intermetallics in Aluminum Alloy Microstructure Under Thin Aqueous Adlayers: A combined DFT and Experimental Study
Open this publication in new window or tab >>Volta Potential Evolution of Intermetallics in Aluminum Alloy Microstructure Under Thin Aqueous Adlayers: A combined DFT and Experimental Study
Show others...
2018 (English)In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 61, no 9-11, p. 1169-1182Article in journal (Refereed) Published
Abstract [en]

In this work, first-principle density functional theory (DFT) was used to calculate the work function and Volta potential differences between aluminum alloy matrix and two intermetallic phases (Mg2Si and Al2Cu) with varying surface terminations as a function of adhering monolayers (ML) of water. The calculated data were compared with experimental local Volta potential data obtained by the scanning Kelvin probe force microscopy (SKPFM) on a commercial aluminum alloy AA6063-T5 in atmospheric environments with varying relative humidity (RH). The calculations suggest that the surface termination has a major effect on the magnitude and polarity of the Volta potential of both intermetallic phases (IMP’s). The Volta potential difference between the IMP’s and the aluminum matrix decreases when the surface is gradually covered by water molecules, and may further change as a function of adhering ML’s of water. This can lead to nobility inversions of the IMP’s relative to the aluminum matrix. The measured Volta potential difference between both IMP’s and their neighboring matrix is dependent on RH. Natural oxidation in ambient indoor air for 2 months led to a nobility inversion of the IMP’s with respect to the aluminum matrix, with the intermetallics showing anodic nature already in dry condition. The anodic nature of Al2Cu remained with the introduction of RH, whereas Mg2Si became cathodic at high RH, presumably due to de-alloying of Mg and oxide dissolution. The DFT calculations predicted an anodic character of both IMP’s in reference to the oxidized aluminum matrix, being in good agreement with the SKPFM data. The DFT and SKPFM data were discussed in light of understanding localized corrosion of aluminum alloys under conditions akin to atmospheric exposure.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-264003 (URN)10.1007/s11244-018-0939-9 (DOI)000435827900037 ()2-s2.0-85045260197 (Scopus ID)
Note

QC 20191125

Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-11-25Bibliographically approved
3. Co-adsorption of H2O, OH, and Cl on aluminum and intermetallic surfaces and its effects on the work function studied by DFT calculations
Open this publication in new window or tab >>Co-adsorption of H2O, OH, and Cl on aluminum and intermetallic surfaces and its effects on the work function studied by DFT calculations
2019 (English)In: Molecules, ISSN 1420-3049, E-ISSN 1420-3049Article in journal (Refereed) Accepted
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-264004 (URN)
Note

QC 20191122

Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-11-22Bibliographically approved
4. Density-functional theory investigation of Al pitting corrosion in electrolyte containing chloride ions
Open this publication in new window or tab >>Density-functional theory investigation of Al pitting corrosion in electrolyte containing chloride ions
Show others...
2015 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 357, p. 2028-2038Article in journal (Refereed) Published
Abstract [en]

The behavior of chloride ions (Cl-) and oxygen species (the oxygen atom, O or molecular oxygen, O-2) on Al(1 1 1) surface has been studied by density functional theory calculations in order to deepen the molecular understanding of fundamental processes leading to pitting of aluminum (Al). The adsorption behavior of individual species, Cl-, O atom and O-2 was determined first. Subsequently, three possible scenarios in different pitting stages were modeled exploring the repassivation and dissolution of Al in neutral electrolyte containing Cl-. In scenario i, it was found that Cl- can hardly destroy even an O-monolayer on Al(1 1 1) surface, however may lead to the elongation of Al-O bond and the weakened binding between the first Al layer and subsequent Al layers. Both O-2 and Cl- were simultaneously introduced onto Al(1 1 1) in scenario ii. The result showed a weakened Al-O interaction and an intensive hybridization peak at -0.18 Ha between Al-3p with Cl-3p suggesting insufficient repassivation behavior of Al under this condition. Finally, scenario iii mimicked different local environmental conditions in pits formed on Al. At low coverage of Cl-, chloride ions had little effect on surface relaxation. The interaction among chloride ions and Al surface became stronger as Cl- coverage increased. Surface Al atoms dissolved gradually and substructures such as AlCl3 and Al2C15 formed when the coverage was larger than 2/3 ML of a monolayer.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Al pitting; DFT calculations; Chloride ions; Electronic interactions
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-264005 (URN)10.1016/j.apsusc.2015.09.180 (DOI)000366219700092 ()2-s2.0-84945550054 (Scopus ID)
Note

QC 20191122

Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-11-22Bibliographically approved
5. The corrosive influence of chloride ions preference adsorption on α-Al2O3(0001) surface
Open this publication in new window or tab >>The corrosive influence of chloride ions preference adsorption on α-Al2O3(0001) surface
2015 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 347, p. 386-391Article in journal (Refereed) Published
Abstract [en]

Conductor-like screening model (COSMO), Periodic DFT calculations have been performed on a Al2O3 surface to model the influence of preference adsorption and interaction of chloride ions at increasing monolayer coverage on undefective passive film on Aluminum in solution environment. The results evidence that the critical monolayer of Cl- is 3/7, which is redefined. With increasing Cl- adsorption, both the first and second Cl- move from Al(1) atop and bridge10 sites to O(5) sites, suggesting that the weaker interaction between Cl- and Al2O3 surface but stronger interactions between three ions make the electrons uniformly occupy on the energy levels of them. More calculations shows that the preference adsorption sites of Cl- are independent of the surface area of oxide, and the adsorption energy decrease in three steps, each adsorption energy step only relate to the adsorption site and the morphology. On undefective oxide film, low coverage Cl- adsorption would restrain surface breakdown to happen which is consistent with the experiment results.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Chloride ion adsorption, Aluminum oxide film, Surface corrosion
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-264006 (URN)10.1016/j.apsusc.2015.04.088 (DOI)000356058500050 ()2-s2.0-84964325831 (Scopus ID)
Note

QC 20191121

Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-11-21Bibliographically approved
6. A DFT-Study of Cl Ingress into α-Al2O3(0001) and Al(111) and Its Possible Influence on Localized Corrosion of Al
Open this publication in new window or tab >>A DFT-Study of Cl Ingress into α-Al2O3(0001) and Al(111) and Its Possible Influence on Localized Corrosion of Al
2019 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, no 11, p. C3124-C3130Article in journal (Refereed) Published
Abstract [en]

Ingress of chloride into alpha-Al2O3(0001) and Al(111) was calculated by first-principles theory calculations by considering Cl insertion into Al or O vacancies within alpha-Al2O3(0001) or into vacancy or interstitial sites within Al(111). For alpha-Al2O3, the formation of an O vacancy is energetically more favorable than of an Al vacancy. The insertion of Cl into an O vacancy is also more favorable than into an Al vacancy. A high energy-barrier has been derived for Cl transport within the neighboring O vacancies. In addition, the work function decreases with Cl ingress into the interior of the oxide. For Al(111), Cl insertion into either an Al vacancy or an interstitial site is less favorable compared to the insertion into alpha-Al2O3. The work function only changes slightly with Cl insertion into an Al vacancy. Moreover, the pre-inserted Cl reduces the energy-barrier for further Cl ingress into alpha-Al2O3, whereas Cl tends to stay in the sub-surface layer of Al(111), suggesting Cl accumulation at the Al2O3/Al.

Place, publisher, year, edition, pages
Electrochemical Society, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-251275 (URN)10.1149/2.0161911jes (DOI)000465526200002 ()2-s2.0-85073451731 (Scopus ID)
Note

QC 20191121

Available from: 2019-05-15 Created: 2019-05-15 Last updated: 2019-11-21Bibliographically approved

Open Access in DiVA

thesis(2900 kB)11 downloads
File information
File name FULLTEXT02.pdfFile size 2900 kBChecksum SHA-512
bd976bbe44c34b92493b7642d80f5bc66bec98415a2a3668f625ce457b749264ea8356067d35f6745099644d57a7cb593ee6f67125e818d5120fbe94e8202818
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Liu, Min
By organisation
Surface and Corrosion Science
Physical Chemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 11 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 51 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf