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Micro-galvanic effects and corrosion inhibition of copper-zinc alloys
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

   With the advancement and accessibility of local probing techniques that can operate at the submicron scale it has become possible to analyse the local corrosion properties of industrially important metallic materials and relate these properties to microstructure characteristics of the same materials. In this doctoral study the focus has been on copper-zinc samples, both as industrial brass alloys and as micro-patterned copper-zinc samples. They have been exposed to dilute chloride solutions and to an atmosphere that mimics indoor conditions that cause corrosion. The main goal has been to investigate micro-galvanic effects caused by surface heterogeneities in the copper-zinc samples, and the corrosion inhibition ability of a self-assembled octadecanethiol (ODT, CH3(CH2)17SH) monolayer when applied to these heterogeneous samples. The local chemistry, local electrochemistry, and local surface chemistry in the presence of the copper-zinc galvanic couplings have been elucidated, and their importance has been investigated for corrosion initiation, propagation, termination, and inhibition. A broad spectrum of local probe techniques has been utilised. They include optical microscopy (ex situ and in situ), electrochemical techniques, scanning electron microscopy with energy dispersive spectroscopy, atomic force microscopy, scanning Kelvin probe force microscopy and confocal Raman spectroscopy. In addition, infrared reflection absorption spectroscopy (in situ) and vibrational sum frequency spectroscopy have been employed to analyse the formation of corrosion products and monitor the corrosion kinetics.

   A characteristic selective zinc dissolution process was triggered in non-metallic inclusions when a brass alloy was exposed to 1 mM NaCl. Disc-like corrosion areas spread radially outwards from the inclusions, the shape and termination of which was attributed to accessibility to chloride ions. An ODT-layer deposited on brass retarded access to chloride ions at the brass surface and slowed down the radial corrosion process. Instead a delayed formation of filiform-like corrosion was observed.

   Upon exposure of the copper-zinc patterned sample to humidified air containing formic acid, micro-galvanic effects were induced by the copper patches on zinc that accelerated the zinc dissolution in the thin aqueous adlayer with concomitant precipitation of zinc formate. The micro-galvanic effects not only resulted in accelerated corrosion rates for zinc, but also in broadening of shapes and atomic structures for the corrosion products formed. Crystalline zinc oxide and zinc formate were observed on the copper-zinc patterned samples, whereas amorphous zinc oxide and zinc formate were formed on the bare zinc surface. Micro-galvanic effects occurred in the two-phase Cu40Zn (Cu with 40 wt% Zn) brass alloy as well, induced by more zinc-rich beta-phase grains surrounded by an alpha matrix with lower zinc-content.

   The application of a self-assembled monolayer of ODT for corrosion inhibition of pure zinc and the patterned copper-zinc samples was also explored. In situ infrared reflection absorption spectroscopy analyses showed that ODT initially reduced the rate of zinc formate formation on pure zinc and on the copper-zinc micro-patterned sample. However, the inhibition efficiency was slightly reduced with exposure time due to local removal of ODT on pure zinc and on the micro-patterned samples. This caused micro-galvanic effects that resulted in increased rates of zinc formate formation on the ODT-covered samples – even higher than on the uncovered samples. When applied to the single-phase Cu20Zn alloy, ODT resulted in a corrosion inhibition that was comparable to that of pure copper, a metal for which ODT has shown very good corrosion inhibition. On double-phase Cu40Zn local galvanic effects resulted in less efficient corrosion inhibition and more abundant corrosion products than on Cu20Zn. Based on vibrational sum frequency spectroscopy, the ODT-layer retained its well-ordered molecular structure throughout the exposure to both Cu20Zn and Cu40Zn.

   In all, the inhibiting action of the ODT-layer was attributed to the transport hindrance of corrosion promoters (O2, H2O, and HCOOH) to the brass surface. This result suggests that ODT can function as a temporary corrosion inhibitor for brass exposed to benign indoor environments. 

Abstract [sv]

   Med utvecklingen av och tillgången till lokala analysmetoder som kan ge information med en lateral upplösning på mindre än en mikrometer har det blivit möjligt att analysera lokala korrosionsegenskaper hos industriellt viktiga metalliska material och relatera dessa egenskaper till mikrostrukturen hos samma material. I doktorsavhandlingen har denna möjlighet utnyttjats för koppar-zinkprover, dels som industriella mässingslegeringar dels som mikro-mönstrade koppar-zinkprover, som exponerats för utspädda kloridlösningar samt för en atmosfär som kan efterlikna den atmosfäriska korrosionen inomhus. Det huvudsakliga målet har varit att undersöka dels mikro-galvaniska korrosionseffekter som orsakas av heterogeniteter på koppar-zinkytorna dels korrosionsförmågan hos självorganiserande monolager av oktadekantiol (ODT, CH3(CH2)17SH) vid adsorption på dessa heterogena ytor. På så vis har den lokala kemin, ytkemin och elektrokemin kunnat klarläggas i närvaro av galvaniska effekter, och dess betydelse har undersökts för korrosionsprocessens initiering, propagering, terminering och inhibering. Ett brett spektrum av lokala analysmetoder har utnyttjats. De innefattar ljusoptisk mikroskopi (ex situ och in situ), elektrokemiska metoder, svepelektronmikroskopi med energidispersiv röntgen-spektroskopi, atomkraftsmikroskopi för mikro-kartering och Voltapotentialmätningar samt konfokal Raman-spektroskopi. Dessutom har infrarödreflektions absorptionsspektroskopi (in situ) och vibrationssummafrekvens spektroskopi (engelska: vibrational sum frequency generation) använts.

   När en mässingslegering exponerades för 1 mM NaCl observerades en selektiv utlösning av zink med karakteristiskt utseende som växte radiellt från icke-metalliska inneslutningar för att bilda cirkulärt formade korrosionsområden. Formen och termineringen av denna korrosionsprocess bestäms av tillgången på kloridjoner. När ett monolager av ODT adsorberades på mässingslegeringen hämmades tillgången av kloridjoner på mässingsytan och den radiella korrosionsprocessen stannade upp. Istället iakttogs en fördröjd bildning av s.k. filiform korrosion.

   Vid exponering av mikro-mönstrade koppar-zinkprover för befuktad luft med låga tillsatser av myrsyra inducerades mikro-galvaniska effekter i gränsen mellan koppar och zink som accelererade utlösningen av zink i den adsorberade fuktfilmen på provet, under samtidig utfällning av zinkformat. De mikro-galvaniska effekterna resulterade inte bara i förhöjda korrosionshastigheter jämfört med de på ren zink, utan även i andra faser hos bildade korrosionsprodukter. På de mikro-mönstrade koppar-zinkproverna bildades kristallint zinkoxid och zinkformat, under det att amorft zinkoxid och zinkhydroxyformat bildades på ren zink. Mikrogalvaniska effekter observerades även i den tvåfasiga mässingslegeringen Cu40Zn (Cu med 40 vikt-% Zn) orsakade av kontakten mellan den mer zinkrika beta-fasen och den omgivande alfa-fasen med lägre zinkhalt.

   Appliceringen av ett självorganiserat monolager av ODT för korrosionsinhibering av ren zink och koppar-zinkprover har också undersöks. In situ infrarödreflektions absorptionsspektroskopi visade att adsorberat ODT initialt hämmade bildningen av zinkformat på ren zink och på de mikro-mönstrade koppar-zinkproverna. Med tiden minskade ODTs korrosionsinhiberings-förmåga på grund av att ODTs vidhäftning lokalt försvann. De mikro-galvaniska effekter som därigenom uppstod resulterade i bildandet av zinkformat som med tiden blev snabbare på de ODT-belagda proverna än på motsvarande prover utan ODT. När ODT applicerades på den enfasiga mässingslegeringen Cu20Zn resulterade detta i en korrosionsinhibering som var jämförbar med den på ren koppar, en metall på vilken ODT tidigare visat mycket bra korrosionsskydd. På den tvåfasiga mässingslegeringen Cu40Zn ledde lokala galvaniska effekter till en mindre effektiv korrosions-inhibering och en rikligare mängd korrosionsprodukter än på Cu20Zn. Baserat på vibrationssummafrekvens spektroskopi behöll ODT-lagret dess välordnade struktur under hela exponeringen på både Cu20Zn och Cu40Zn.

   ODTs korrosionsinhibering tillskrivs främst transport-hämningen av korrosionsstimulatorer (O2, H2O och HCOOH) till mässingsytan och antyder att ODT kan fungera som en temporär korrosionsinhibitor för mässing i milda inomhusmiljöer.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2014. , xxii, 82 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:31
Keyword [en]
Copper, zinc, brass, octadecanethiol, IR Spectroscopy, AFM, atmospheric corrosion, aqueous corrosion, corrosion inhibition
Keyword [sv]
Koppar, zink, mässing, oktadekantiol, IR-reflektions absorptionsspektroskopi, AFM, atmosfärisk korrosion, vattenaktig korrosion, korrosionsinhibering.
National Category
Chemical Sciences
Research subject
Chemical Engineering; Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-151189ISBN: 978-91-7595-227-7 (print)OAI: oai:DiVA.org:kth-151189DiVA: diva2:746995
Public defence
2014-09-25, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2009-3240
Note

QC 20140915

Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2014-09-16Bibliographically approved
List of papers
1. Radial Spreading of Localized Corrosion-Induced Selective Leaching on alpha-Brass in Dilute NaCl Solution
Open this publication in new window or tab >>Radial Spreading of Localized Corrosion-Induced Selective Leaching on alpha-Brass in Dilute NaCl Solution
2013 (English)In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 69, no 5, 468-476 p.Article in journal (Refereed) Published
Abstract [en]

The radial spreading of selective leaching on an a-brass alloy, Cu20Zn, in diluted sodium chloride (NaCl) has been followed in situ by light optical microscopy. The corrosion process initiates through localized dissolution of micrometer-sized, Zn-rich areas. These areas initially act as anodes, where the Zn will dissolve as Zn2+. The continued growth is a highly dynamic process, involving dezincification that results in local ennoblement of initial anode areas and changes in the local chemistry of the solution. These changes drive the anodic area outward to form a ring-shaped anode with an increasing diameter. At a sufficiently high local Cl- ion concentration, Cu dissolves as CuCl2-, whereby the radial growth continues. At critical minimum local Cl- ion concentration, the radial growth is terminated.

Keyword
leaching, light optical microscopy, localized corrosion, sodium chloride
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-123622 (URN)10.5006/0611 (DOI)000318619600004 ()2-s2.0-84877678067 (Scopus ID)
Funder
Swedish Research Council, 621-2009-3240
Note

QC 20130614

Available from: 2013-06-14 Created: 2013-06-13 Last updated: 2017-12-06Bibliographically approved
2. Micro-galvanic corrosion effects on patterned copper-zinc samples during exposure in humidified air containing formic acid
Open this publication in new window or tab >>Micro-galvanic corrosion effects on patterned copper-zinc samples during exposure in humidified air containing formic acid
Show others...
2013 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 160, no 9, C423-C431 p.Article in journal (Refereed) Published
Abstract [en]

Corrosion in indoor atmospheric environments is often triggered by carboxylic acids, especially at higher relative humidity. Microgalvanic effects can lead to severe corrosion, particularly important in miniature devices with small-sized metallic components. To elucidate the mechanism of micro-galvanic corrosion effects, well-defined zinc-copper patterned samples were investigated during exposure to 100 ppb formic acid (HCOOH) and 80% relative humidity at 20°C. The corrosion effects were monitored quantitatively with in situ infrared absorption spectroscopy, and the corrosion products characterized with scanning electron microscopy, confocal Raman microscopy, and atomic force microscopy. The nature of corrosion on zinc on the patterned samples was compared with that on pure zinc and turned out to result, not only in several times higher corrosion kinetics, but also in different corrosion products with respect to distribution, morphology, and composition. Local electrochemical and chemical gradients across the copper-zinc borders resulted in characteristic hemispherically shaped corrosion products at the zinc-copper junction, and in the formation of zinc formate dihydrate (Zn(HCOO)2 · 2H 2O) and crystalline zinc oxide (ZnO), phases not identified on pure zinc. In all, the micro-galvanic effects on the patterned samples resulted in accelerated corrosion kinetics and in structurally more developed corrosion products.

Keyword
Accelerated corrosion, Atmospheric environment, Chemical gradients, Confocal Raman microscopy, Corrosion kinetics, Corrosion products, Higher relative humidity, Metallic component
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-133863 (URN)10.1149/2.113308jes (DOI)000324600600052 ()2-s2.0-84881512858 (Scopus ID)
Funder
Swedish Research Council, 621-2009-3240 348-2008-6078
Note

QC 20131113

Available from: 2013-11-13 Created: 2013-11-11 Last updated: 2017-12-06Bibliographically approved
3. Octadecanethiol as Corrosion Inhibitor for Zinc and Patterned Zinc-Copper in Humidified Air with Formic Acid
Open this publication in new window or tab >>Octadecanethiol as Corrosion Inhibitor for Zinc and Patterned Zinc-Copper in Humidified Air with Formic Acid
2014 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 161, no 6, C330-C338 p.Article in journal (Refereed) Published
Abstract [en]

The corrosion inhibition efficiency of octadecanethiol (ODT) for zinc and a zinc-copper patterned model sample (Zn-Cu) has been explored during exposure in an atmosphere that mimics indoor atmospheric corrosion containing humidified air (80% relative humidity at 20 degrees C) and formic acid (around 100 ppb). The corrosion kinetics were monitored in situ with infrared reflection absorption spectroscopy, and the local nature of corrosion effects post-analyzed with complementary scanning electron microscopy, atomic force microscopy and confocal Raman spectroscopy. ODT shows initially a corrosion inhibiting ability both on zinc and on Zn-Cu. This ability decreases with time due to local removal of ODT, which causes micro-galvanic effects that eventually result in corrosion rates that exceed those for the uncovered samples. On bare and ODT-covered samples, the presence of a copper-zinc junction results in both accelerated corrosion and in structurally more developed corrosion products. Overall, the results suggest that ODT can function as a temporary corrosion inhibitor in representative indoor environments on zinc and zinc with zinc-copper junctions.

Keyword
Initial Atmospheric Corrosion, Sum-Frequency Spectroscopy, Reflection-Absorption-Spectroscopy, Alkanethiol-Covered Copper, Self-Assembled Monolayers, Carboxylic-Acids, Acetic-Acid, Generation Spectroscopy, Adsorption, Oxidation
National Category
Other Chemistry Topics Materials Engineering
Identifiers
urn:nbn:se:kth:diva-149519 (URN)10.1149/2.089406jes (DOI)000339508600070 ()2-s2.0-84904795162 (Scopus ID)
Funder
Swedish Research Council, 621-2009-3240
Note

QC 20140822

Available from: 2014-08-22 Created: 2014-08-22 Last updated: 2017-12-05Bibliographically approved
4. The atmospheric corrosion inhibition of octadecanethiol adsorbed on two brass alloys exposed to humidified air with formic acid
Open this publication in new window or tab >>The atmospheric corrosion inhibition of octadecanethiol adsorbed on two brass alloys exposed to humidified air with formic acid
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Self-assembled monolayers of octadecanethiol (ODT) have previously shown to provide excellent corrosion inhibition on copper exposed to humidified air containing formic acid - mimicking indoor atmospheric corrosion. ODT layers are, however, much less efficient corrosion inhibitors for zinc. In this work we elucidate the possibility of using ODT monolayers to inhibit corrosion of brass. We find that ODT provides equally good corrosion inhibition of single-phase Cu20Zn as of pure copper, retarding the transport of corrosion stimulators to the brass surface. On double-phase Cu40Zn, however, local galvanic effects lead to less efficient corrosion inhibition and more corrosion products than on Cu20Zn.

Keyword
Brass, IR spectroscopy, AFM, SEM, Atmospheric corrosion, Interfaces
National Category
Analytical Chemistry Materials Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-151186 (URN)
Note

Submitted to ECS 2014. QS 2014

Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2017-03-02Bibliographically approved

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