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A Molecular view of inital Atmospheric Corrosion: In situ surface studies of zinc based on vibrational spectroscopy
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. (Yt- och Korrosionsvetenskap)ORCID iD: 0000-0003-2100-8864
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Atmospheric corrosion takes place on most metals as they interact with thesurrounding environment. A degradation of the metal is the common result,which often leads to a shortened lifespan of the material. Hence, knowledge onthe fundamental interaction between a gas containing corrosive constituentsand a metal surface, which is the starting point of atmospheric corrosion, isimportant in many contexts. As the nature of atmospheric corrosion is inherentlycomplex, it imposes demands on the analytical studies that are neededin order to understand the fundamentals on a molecular level. Consequently,in-situ vibrational techniques, providing molecular information, have beenutilized in this work to study atmospheric corrosion by targeting the initialstages of the interaction between corrosive air and a metal surface. The initialstages (from minutes until days of exposure) were studied as these havea large influence on the atmospheric corrosion for prolonged exposure times.

More specifically, the interaction between humidified air to which organicacids were added, and zinc was targeted in order to address a situation inindoor atmospheric corrosion, where organic acids are of importance. Zinc isa constituent in e.g. brass, which is an alloy used in many indoor applications.

A systematic investigation utilizing complementary acting vibrational techniquesthus enabled detailed information on the mechanisms of the onsetof atmospheric corrosion of zinc induced by acetic and formic acid. Corrosionproducts of both two dimensional and three dimensional character couldbe separately studied by combining VSFS (interface sensitive), IRAS (nearsurfacesensitive), and CRM (bulk sensitive).

The Zn surface was found to be heterogeneous with different hydroxylgroups present on the surface. As this surface was exposed to formic or aceticacid, the OH groups on the surface were rapidly displaced in a ligand exchangewith formate or acetate. These ligands, organised in two dimensionalstructures, promoted corrosion by weakening the bonds of the Zn atoms totheir surrounding matrix.

The subsequent growth of three dimensional corrosion products, Zn hydroxyacetate and formate, observed within short exposure times of Zn exposedto acetic and formic acid, was found to be electrochemical in nature.Cathodic areas consisting of more crystalline ZnO were observed. The potentialdifference between these more noble areas on the surface and those of lessnoble character created an electrochemical cell, initiating release of Zn ionsinto the aqueous adlayer in the anodic reactions. These Zn ions precipitatedas localised corrosion products. The cathodic areas increased the local pHon the surface, thereby promoting precipitation in their vicinity. The resultson initial stages of this type of corrosion were found to have similarities withprevious field studies of Zn exposed to real indoor environments.

One way to decrease the corrosion rate of zinc is by adsorbing a corrosioninhibitor to the metal surface in order to protect it. As a model for sucha corrosion inhibitor, octadecanethiol (CH3(CH2)17SH) was seen to provideincreased corrosion protection of both reduced and oxidised Zn substrates byforming an adsorbed surface layer with an ordered structure.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , xi, 71 p.
Series
TRITA CHE Report, ISSN 1654-1081 ; 2009:60
Keyword [en]
Atmospheric corrosion, zinc, vibrational spectroscopy, formic acid, acetic acid
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-11729ISBN: 978-91-7415-499-3 (print)OAI: oai:DiVA.org:kth-11729DiVA: diva2:280073
Public defence
2009-12-11, F3, Lindstdtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100719Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2010-07-19Bibliographically approved
List of papers
1. Adsorption and Structure of Octadecanethiol on Zinc Surfaces As Probed by SumFrequency Generation Spectroscopy, Imaging, and Electrochemical Techniques
Open this publication in new window or tab >>Adsorption and Structure of Octadecanethiol on Zinc Surfaces As Probed by SumFrequency Generation Spectroscopy, Imaging, and Electrochemical Techniques
2007 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 47, 17587-17596 p.Article in journal (Refereed) Published
Abstract [en]

Octadecanethiol (ODT) adsorbed onto zinc has been studied with sum frequency generation (SFG), sum frequency generation imaging microscopy (SFG-IM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrical impedance spectroscopy (EIS) in order to investigate its corrosion protective ability and conformational ordering. SFG shows that ODT forms an ordered adsorbate on both reduced and oxidized zinc within short times after immersion in 1 mM ODT/ethanol solution. The corrosion protection, deduced by EIS, is also improved after immersion in the ODT solution. After longer immersion times, the corrosion protection decreases as well as the conformational order of the adsorbed ODT. Increasing the ODT concentration avoids this degradation with prolonged immersion time. The ODT is seen in the XPS spectra to adsorb to the reduced as well as the oxidized zinc by forming a Zn-S bond for both short and long immersion times. The SFG-IM completes the picture, showing a heterogeneous surface with areas corresponding to ordered ODT as well as disordered or uncovered regions. The density of adsorbed ODT after 24 h immersion time for both reduced and oxidized zinc was deduced from CV and was found to be approximately 6.7 x 10(-9) mol/cm(2).

Keyword
self-assembled monolayers; ray photoelectron-spectroscopy; vibrational spectroscopy; alkanethiol monolayers; impedance spectroscopy; molecular-orientation; zno nanoparticles; stretching modes; single-crystal; spectrum
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-11723 (URN)10.1021/jp075286+ (DOI)000251141100021 ()2-s2.0-37049013707 (Scopus ID)
Note
QC 20100719Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2017-12-12Bibliographically approved
2. Initial Atmospheric Corrosion of Zn: Influence of Humidity on the Adsorption of Formic Acid Studied by Vibrational Sum Frequency Spectroscopy
Open this publication in new window or tab >>Initial Atmospheric Corrosion of Zn: Influence of Humidity on the Adsorption of Formic Acid Studied by Vibrational Sum Frequency Spectroscopy
2009 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, 6169-6173 p.Article in journal (Refereed) Published
Abstract [en]

The ZnO/Zn surface exposed to formic acid undergoes a partial, reversible dissociation to formate ion, and a protonated surface oxide and is seen to have different hydration states depending on the relative humidity. Under high relative humidity conditions it exists as a formate coordinated to the surface with the oxygen atoms toward the surface and the C-H directed away into the vapor. In a dry environment a formic acid/formate intermediate is formed, although a substantial amount of dissociated species still are present, in both hydrated and nonhydrated form. The results may have implications on the initial atmospheric corrosion of Zn and emphasize that the ZnO/Zn surface is heterogeneous with a range of acid and basic sites for the adsorption of formate and the proton.

Keyword
reflection-absorption spectroscopy; organic-constituents; oxide surfaces; in-situ; water; formate; zinc; spectra; raman; interfaces
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-11725 (URN)10.1021/jp900459q (DOI)000265030200044 ()2-s2.0-65249148580 (Scopus ID)
Note
QC 20100719Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2017-12-12Bibliographically approved
3. Initial Atmospheric Corrosion of Zinc Exposed to Formic Acid, Investigated by in Situ Vibrational Sum Frequency Spectroscopy and Density Functional Theory Calculations
Open this publication in new window or tab >>Initial Atmospheric Corrosion of Zinc Exposed to Formic Acid, Investigated by in Situ Vibrational Sum Frequency Spectroscopy and Density Functional Theory Calculations
2008 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, 2088-2095 p.Article in journal (Refereed) Published
Abstract [en]

Vibrational sum frequency spectroscopy (VSFS) and ab initio density functional theory (DFT) calculations of formic acid on ZnO/Zn have been performed in order to understand the first step of atmospheric corrosion on zinc initiated by formic acid. In addition, infrared reflection absorption spectroscopy (IRAS) has been employed to complement the surface sensitive VSFS results to identify the corrosion products. Oxidized polycrystalline zinc samples were exposed to 120 ppb formic acid in either humid or dry Air where, the formic acid adsorption on ZnO/Zn is observed to have a low dependence on the humidity, as deduced by VSFS. Formate is formed on the surface in both dry and humid air and stabilized in configuration after about 90 min exposure in 120 ppb formic acid as seen in the VSFS results. This is evidenced by the occurrence of the CH and symmetric COO- vibrations of the formate ion. The DFT calculations support the VSFS results, showing a coordination of the formate to zinc ions without participation from water molecules.

Keyword
reflection-absorption spectroscopy; liquid-gas interface; acetic-acid; organic-constituents; sfg spectroscopy; ni(110) surface; water mixtures; sulfur-dioxide; film growth; metal
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-11724 (URN)10.1021/jp805582h (DOI)000263134700009 ()2-s2.0-84962469268 (Scopus ID)
Note
QC 20100719Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2017-12-12Bibliographically approved
4. Molecular in-situ observations of hydroxyl groups and ligand exchange during initial atmospheric corrosion
Open this publication in new window or tab >>Molecular in-situ observations of hydroxyl groups and ligand exchange during initial atmospheric corrosion
(English)Manuscript (preprint) (Other academic)
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-11726 (URN)
Note
QC 20100719Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2010-07-19Bibliographically approved
5. Molecular structural information of the atmospheric corrosion of zinc studied by vibrational spectroscopy techniques: Part I. Experimental approach
Open this publication in new window or tab >>Molecular structural information of the atmospheric corrosion of zinc studied by vibrational spectroscopy techniques: Part I. Experimental approach
(English)Manuscript (preprint) (Other academic)
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-11727 (URN)
Note
QC 20100719Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2010-07-19Bibliographically approved
6. Molecular structural information of the atmospheric corrosion of zinc studied by vibrational spectroscopy techniques: Part II. Two and three dimensional growth of reaction products induced by formic and acetic acid
Open this publication in new window or tab >>Molecular structural information of the atmospheric corrosion of zinc studied by vibrational spectroscopy techniques: Part II. Two and three dimensional growth of reaction products induced by formic and acetic acid
(English)Manuscript (preprint) (Other academic)
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-11728 (URN)
Note
QC 20100719Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2010-07-19Bibliographically approved

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