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The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel / CALLUM GALLAGHER

Swansea University Author: CALLUM GALLAGHER

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DOI (Published version): 10.23889/SUthesis.59489

Abstract

This work set out to elucidate the microstructural corrosion mechanisms of sacrificial corrosion coating, Galvalloy® (Zn-4.8wt.%Al), which is used extensively in the strip steel industry. Corrosion of Galvalloy® occurs at the surface, where only Galvalloy® is exposed, and the cut edge, where Galvall...

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Published: Swansea 2022
Institution: Swansea University
Degree level: Doctoral
Degree name: EngD
Supervisor: Sullivan, James H.
URI: https://cronfa.swan.ac.uk/Record/cronfa59489
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fullrecord <?xml version="1.0"?><rfc1807><datestamp>2022-03-03T18:24:15.4633615</datestamp><bib-version>v2</bib-version><id>59489</id><entry>2022-03-03</entry><title>The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel</title><swanseaauthors><author><sid>022a999bcd7fbe4285e7705501d1d5ca</sid><firstname>CALLUM</firstname><surname>GALLAGHER</surname><name>CALLUM GALLAGHER</name><active>true</active><ethesisStudent>false</ethesisStudent></author></swanseaauthors><date>2022-03-03</date><abstract>This work set out to elucidate the microstructural corrosion mechanisms of sacrificial corrosion coating, Galvalloy&#xAE; (Zn-4.8wt.%Al), which is used extensively in the strip steel industry. Corrosion of Galvalloy&#xAE; occurs at the surface, where only Galvalloy&#xAE; is exposed, and the cut edge, where Galvalloy&#xAE; and steel are coupled, which increases the corrosion rate of Galvalloy&#xAE;. Chapter 3 demonstrates the time-lapse microscopy (TLM) technique being used to analyse, in-situ, the microstructural mechanism of surface and cut-edge corrosion of Galvalloy&#xAE; immersed in pH 7 1 wt.% NaCl. Rotating disk electrode (RDE) and potentiodynamic polarisation (PD) tests were performed on the individual phases of Galvalloy&#xAE; to identify their anodic and cathodic activity in 1 wt.% NaCl. TLM showed that surface corrosion initiates and propagates through the binary eutectic Zn-Al phase, whereas cut-edge corrosion initiates within the primary zinc dendrite phase and proceeding through the entire microstructure. The electrochemical data validated this as the RDE showed that the Al containing phases could not support cathodic activity as well as the primary zinc phases and PD showed that the zinc phases are more susceptible to anodic dissolution when polarised. Chapter 4 investigated, using TLM and PD, the corrosion rate and mechanism of the Galvalloy&#xAE; surface across pH 3, 7, 10 and 13 in 1 wt. % NaCl. At pH 3 and 13, D showed a maxima of corrosion rate was seen and TLM illustrated no precipitation of corrosion product. PD showed pH 7 having the lowest icorr, however, the precipitated corrosion product formed at a smaller radius relative to active anodes during TLM experiments of pH 10 compared to pH 7. Chapter 5 utilized ZRA and TLM to investigate the rate and mechanism of the corrosion of Galvalloy&#xAE; next to a steel &#x2018;cut-edge&#x2019; across pH 3, 7, 10 and 13 in 1 wt. % NaCl. The corrosion rate of Galvalloy&#xAE; was greater compared to the surface corrosion, due to the polarisation imposed by the connection to the steel substrate and the same corrosion rate to pH trend in Chapter 4 was see. At pH 7, 10 and 13, corrosion initiation occurs in the zinc dendrites, whereas at pH 3 the corrosion is generalised. Chapter 6 investigated the effect of increasing steel to Galvalloy&#xAE; on the corrosion rate of Galvalloy&#xAE; at pH 7 in 1 wt.% NaCl using ZRA and TLM. ZRA demonstrated a linear trend, whereas TLM showed a non-linear trend which is suggested to be due to the increased ease of precipitation in the experimental set-up. Chapter 7 is an example of a real-world corrosion problem involving organically coated Galvalloy&#xAE;. 2 &#xB5;L of HCl, FeCl2, NaCl and Acetic acid (CH3OOH) were administered to a scribed region of PVB coated Galvalloy&#xAE; and exposed to a high relative-humidity environment for a month to induce under-film corrosion in order to compare the results to deduce which salt was responsible for the real-world corrosion. NaCl was the salt that posed the greatest similarity and cathodic delamination is the postulated corrosion mechanism.</abstract><type>E-Thesis</type><journal/><volume/><journalNumber/><paginationStart/><paginationEnd/><publisher/><placeOfPublication>Swansea</placeOfPublication><isbnPrint/><isbnElectronic/><issnPrint/><issnElectronic/><keywords>Corrosion, coatings, galvanised, microscopy, electrochemistry, zinc, aluminium, strip steel</keywords><publishedDay>3</publishedDay><publishedMonth>3</publishedMonth><publishedYear>2022</publishedYear><publishedDate>2022-03-03</publishedDate><doi>10.23889/SUthesis.59489</doi><url/><notes>A selection of third party content is redacted or is partially redacted from this thesis due to copyright restrictions.ORCiD identifier: https://orcid.org/0000-0001-6005-2775</notes><college>COLLEGE NANME</college><CollegeCode>COLLEGE CODE</CollegeCode><institution>Swansea University</institution><supervisor>Sullivan, James H.</supervisor><degreelevel>Doctoral</degreelevel><degreename>EngD</degreename><degreesponsorsfunders>TATA Steel; EPSRC; WEFO; Research grant number COATED2 CDT (EP/L0150991/1)</degreesponsorsfunders><apcterm/><lastEdited>2022-03-03T18:24:15.4633615</lastEdited><Created>2022-03-03T16:45:03.5608614</Created><path><level id="1">Faculty of Science and Engineering</level><level id="2">School of Engineering and Applied Sciences - Uncategorised</level></path><authors><author><firstname>CALLUM</firstname><surname>GALLAGHER</surname><order>1</order></author></authors><documents><document><filename>59489__22510__2696bdc2da02419086c35799e0e431df.pdf</filename><originalFilename>Gallagher_Callum_EngD_Thesis_Final_Redacted.pdf</originalFilename><uploaded>2022-03-03T18:17:28.2689311</uploaded><type>Output</type><contentLength>50656922</contentLength><contentType>application/pdf</contentType><version>Redacted version - open access</version><cronfaStatus>true</cronfaStatus><documentNotes>Copyright: The author, Callum Gallagher, 2022.</documentNotes><copyrightCorrect>true</copyrightCorrect><language>eng</language></document></documents><OutputDurs/></rfc1807>
spelling 2022-03-03T18:24:15.4633615 v2 59489 2022-03-03 The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel 022a999bcd7fbe4285e7705501d1d5ca CALLUM GALLAGHER CALLUM GALLAGHER true false 2022-03-03 This work set out to elucidate the microstructural corrosion mechanisms of sacrificial corrosion coating, Galvalloy® (Zn-4.8wt.%Al), which is used extensively in the strip steel industry. Corrosion of Galvalloy® occurs at the surface, where only Galvalloy® is exposed, and the cut edge, where Galvalloy® and steel are coupled, which increases the corrosion rate of Galvalloy®. Chapter 3 demonstrates the time-lapse microscopy (TLM) technique being used to analyse, in-situ, the microstructural mechanism of surface and cut-edge corrosion of Galvalloy® immersed in pH 7 1 wt.% NaCl. Rotating disk electrode (RDE) and potentiodynamic polarisation (PD) tests were performed on the individual phases of Galvalloy® to identify their anodic and cathodic activity in 1 wt.% NaCl. TLM showed that surface corrosion initiates and propagates through the binary eutectic Zn-Al phase, whereas cut-edge corrosion initiates within the primary zinc dendrite phase and proceeding through the entire microstructure. The electrochemical data validated this as the RDE showed that the Al containing phases could not support cathodic activity as well as the primary zinc phases and PD showed that the zinc phases are more susceptible to anodic dissolution when polarised. Chapter 4 investigated, using TLM and PD, the corrosion rate and mechanism of the Galvalloy® surface across pH 3, 7, 10 and 13 in 1 wt. % NaCl. At pH 3 and 13, D showed a maxima of corrosion rate was seen and TLM illustrated no precipitation of corrosion product. PD showed pH 7 having the lowest icorr, however, the precipitated corrosion product formed at a smaller radius relative to active anodes during TLM experiments of pH 10 compared to pH 7. Chapter 5 utilized ZRA and TLM to investigate the rate and mechanism of the corrosion of Galvalloy® next to a steel ‘cut-edge’ across pH 3, 7, 10 and 13 in 1 wt. % NaCl. The corrosion rate of Galvalloy® was greater compared to the surface corrosion, due to the polarisation imposed by the connection to the steel substrate and the same corrosion rate to pH trend in Chapter 4 was see. At pH 7, 10 and 13, corrosion initiation occurs in the zinc dendrites, whereas at pH 3 the corrosion is generalised. Chapter 6 investigated the effect of increasing steel to Galvalloy® on the corrosion rate of Galvalloy® at pH 7 in 1 wt.% NaCl using ZRA and TLM. ZRA demonstrated a linear trend, whereas TLM showed a non-linear trend which is suggested to be due to the increased ease of precipitation in the experimental set-up. Chapter 7 is an example of a real-world corrosion problem involving organically coated Galvalloy®. 2 µL of HCl, FeCl2, NaCl and Acetic acid (CH3OOH) were administered to a scribed region of PVB coated Galvalloy® and exposed to a high relative-humidity environment for a month to induce under-film corrosion in order to compare the results to deduce which salt was responsible for the real-world corrosion. NaCl was the salt that posed the greatest similarity and cathodic delamination is the postulated corrosion mechanism. E-Thesis Swansea Corrosion, coatings, galvanised, microscopy, electrochemistry, zinc, aluminium, strip steel 3 3 2022 2022-03-03 10.23889/SUthesis.59489 A selection of third party content is redacted or is partially redacted from this thesis due to copyright restrictions.ORCiD identifier: https://orcid.org/0000-0001-6005-2775 COLLEGE NANME COLLEGE CODE Swansea University Sullivan, James H. Doctoral EngD TATA Steel; EPSRC; WEFO; Research grant number COATED2 CDT (EP/L0150991/1) 2022-03-03T18:24:15.4633615 2022-03-03T16:45:03.5608614 Faculty of Science and Engineering School of Engineering and Applied Sciences - Uncategorised CALLUM GALLAGHER 1 59489__22510__2696bdc2da02419086c35799e0e431df.pdf Gallagher_Callum_EngD_Thesis_Final_Redacted.pdf 2022-03-03T18:17:28.2689311 Output 50656922 application/pdf Redacted version - open access true Copyright: The author, Callum Gallagher, 2022. true eng
title The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel
spellingShingle The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel
CALLUM GALLAGHER
title_short The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel
title_full The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel
title_fullStr The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel
title_full_unstemmed The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel
title_sort The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel
author_id_str_mv 022a999bcd7fbe4285e7705501d1d5ca
author_id_fullname_str_mv 022a999bcd7fbe4285e7705501d1d5ca_***_CALLUM GALLAGHER
author CALLUM GALLAGHER
author2 CALLUM GALLAGHER
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publishDate 2022
institution Swansea University
doi_str_mv 10.23889/SUthesis.59489
college_str Faculty of Science and Engineering
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hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Engineering and Applied Sciences - Uncategorised{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Uncategorised
document_store_str 1
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description This work set out to elucidate the microstructural corrosion mechanisms of sacrificial corrosion coating, Galvalloy® (Zn-4.8wt.%Al), which is used extensively in the strip steel industry. Corrosion of Galvalloy® occurs at the surface, where only Galvalloy® is exposed, and the cut edge, where Galvalloy® and steel are coupled, which increases the corrosion rate of Galvalloy®. Chapter 3 demonstrates the time-lapse microscopy (TLM) technique being used to analyse, in-situ, the microstructural mechanism of surface and cut-edge corrosion of Galvalloy® immersed in pH 7 1 wt.% NaCl. Rotating disk electrode (RDE) and potentiodynamic polarisation (PD) tests were performed on the individual phases of Galvalloy® to identify their anodic and cathodic activity in 1 wt.% NaCl. TLM showed that surface corrosion initiates and propagates through the binary eutectic Zn-Al phase, whereas cut-edge corrosion initiates within the primary zinc dendrite phase and proceeding through the entire microstructure. The electrochemical data validated this as the RDE showed that the Al containing phases could not support cathodic activity as well as the primary zinc phases and PD showed that the zinc phases are more susceptible to anodic dissolution when polarised. Chapter 4 investigated, using TLM and PD, the corrosion rate and mechanism of the Galvalloy® surface across pH 3, 7, 10 and 13 in 1 wt. % NaCl. At pH 3 and 13, D showed a maxima of corrosion rate was seen and TLM illustrated no precipitation of corrosion product. PD showed pH 7 having the lowest icorr, however, the precipitated corrosion product formed at a smaller radius relative to active anodes during TLM experiments of pH 10 compared to pH 7. Chapter 5 utilized ZRA and TLM to investigate the rate and mechanism of the corrosion of Galvalloy® next to a steel ‘cut-edge’ across pH 3, 7, 10 and 13 in 1 wt. % NaCl. The corrosion rate of Galvalloy® was greater compared to the surface corrosion, due to the polarisation imposed by the connection to the steel substrate and the same corrosion rate to pH trend in Chapter 4 was see. At pH 7, 10 and 13, corrosion initiation occurs in the zinc dendrites, whereas at pH 3 the corrosion is generalised. Chapter 6 investigated the effect of increasing steel to Galvalloy® on the corrosion rate of Galvalloy® at pH 7 in 1 wt.% NaCl using ZRA and TLM. ZRA demonstrated a linear trend, whereas TLM showed a non-linear trend which is suggested to be due to the increased ease of precipitation in the experimental set-up. Chapter 7 is an example of a real-world corrosion problem involving organically coated Galvalloy®. 2 µL of HCl, FeCl2, NaCl and Acetic acid (CH3OOH) were administered to a scribed region of PVB coated Galvalloy® and exposed to a high relative-humidity environment for a month to induce under-film corrosion in order to compare the results to deduce which salt was responsible for the real-world corrosion. NaCl was the salt that posed the greatest similarity and cathodic delamination is the postulated corrosion mechanism.
published_date 2022-03-03T04:16:50Z
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score 11.012924

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