The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium

Williams, Geraint; Llwyd, Hefin Ap; Subramanian, Raman; McMurray, Neil; McMurray, Hamilton

doi:10.5006/2328

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The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium

Geraint Williams

, Hefin Ap Llwyd Dafydd, Raman Subramanian, Neil McMurray, Hamilton McMurray

Corrosion

Swansea University Authors: Geraint Williams , Hamilton McMurray

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DOI (Published version): 10.5006/2328

Abstract

An empirically derived dependence of an apparent breakdown potential (Eb) of magnesium (Mg) on chloride ion concentration is reported. In situations where spontaneous breakdown in the absence of external polarization is observed, leading to the subsequent propagation of localised corrosion, Eb can b...

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Published in:	Corrosion
ISSN:	0010-9312 1938-159X
Published:	2017
Online Access:	Check full text
URI:	https://cronfa.swan.ac.uk/Record/cronfa31999

first_indexed	2017-02-16T13:38:10Z
last_indexed	2018-02-09T05:19:27Z
id	cronfa31999
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spelling	2017-02-16T11:18:39.9203748 v2 31999 2017-02-16 The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium 0d8fc8d44e2a3c88ce61832f66f20d82 0000-0002-3399-5142 Geraint Williams Geraint Williams true false 56fc1b17ffc3bdf6039dc05c6eba7f2a Hamilton McMurray Hamilton McMurray true false 2017-02-16 EAAS An empirically derived dependence of an apparent breakdown potential (Eb) of magnesium (Mg) on chloride ion concentration is reported. In situations where spontaneous breakdown in the absence of external polarization is observed, leading to the subsequent propagation of localised corrosion, Eb can be determined by following time-dependent changes in free corrosion potential (Ecorr). Breakdown of temporary passivity is marked by a clear inflection in the time-dependent value of Ecorr, characterised by a sharp decrease in potential from a maximum value where Ecorr = Eb. Characterisation of localized corrosion behaviour by in-situ scanning vibrating electrode studies, prior to and following the point of breakdown, is employed to explain the observed Ecorr vs. time characteristics. Examples of typical behaviour upon immersion in aqueous solutions containing different chloride ion concentrations ([Cl-]) are given for commercially pure Mg and an AZ31 alloy. For high purity Mg, which remains passive at pH 11 at all chloride concentrations ≤ 2 mol dm-3, Eb values are determined as a function of chloride ion concentration [Cl-] by means of a potentiodynamic method. In both cases a dependence of Eb on [Cl-] is established such that Eb = A + B log10[Cl-], where the value of B is typically -0.11 V per decade. The practical implications of the existence of a breakdown potential for Mg is considered in terms of the selection of an appropriate chloride ion concentration in standard corrosion tests. Journal Article Corrosion 0010-9312 1938-159X 31 12 2017 2017-12-31 10.5006/2328 COLLEGE NANME Engineering and Applied Sciences School COLLEGE CODE EAAS Swansea University 2017-02-16T11:18:39.9203748 2017-02-16T11:17:23.5258373 Faculty of Science and Engineering School of Engineering and Applied Sciences - Materials Science and Engineering Geraint Williams 0000-0002-3399-5142 1 Hefin Ap Llwyd Dafydd 2 Raman Subramanian 3 Neil McMurray 4 Hamilton McMurray 5 0031999-16022017111825.pdf williams2017(2).pdf 2017-02-16T11:18:25.8170000 Output 1167485 application/pdf Accepted Manuscript true 2017-05-15T00:00:00.0000000 false eng
title	The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium
spellingShingle	The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium Geraint Williams Hamilton McMurray
title_short	The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium
title_full	The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium
title_fullStr	The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium
title_full_unstemmed	The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium
title_sort	The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium
author_id_str_mv	0d8fc8d44e2a3c88ce61832f66f20d82 56fc1b17ffc3bdf6039dc05c6eba7f2a
author_id_fullname_str_mv	0d8fc8d44e2a3c88ce61832f66f20d82_*_Geraint Williams 56fc1b17ffc3bdf6039dc05c6eba7f2a_*_Hamilton McMurray
author	Geraint Williams Hamilton McMurray
author2	Geraint Williams Hefin Ap Llwyd Dafydd Raman Subramanian Neil McMurray Hamilton McMurray
format	Journal article
container_title	Corrosion
publishDate	2017
institution	Swansea University
issn	0010-9312 1938-159X
doi_str_mv	10.5006/2328
college_str	Faculty of Science and Engineering
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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 - Materials Science and Engineering{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Materials Science and Engineering
document_store_str	1
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description	An empirically derived dependence of an apparent breakdown potential (Eb) of magnesium (Mg) on chloride ion concentration is reported. In situations where spontaneous breakdown in the absence of external polarization is observed, leading to the subsequent propagation of localised corrosion, Eb can be determined by following time-dependent changes in free corrosion potential (Ecorr). Breakdown of temporary passivity is marked by a clear inflection in the time-dependent value of Ecorr, characterised by a sharp decrease in potential from a maximum value where Ecorr = Eb. Characterisation of localized corrosion behaviour by in-situ scanning vibrating electrode studies, prior to and following the point of breakdown, is employed to explain the observed Ecorr vs. time characteristics. Examples of typical behaviour upon immersion in aqueous solutions containing different chloride ion concentrations ([Cl-]) are given for commercially pure Mg and an AZ31 alloy. For high purity Mg, which remains passive at pH 11 at all chloride concentrations ≤ 2 mol dm-3, Eb values are determined as a function of chloride ion concentration [Cl-] by means of a potentiodynamic method. In both cases a dependence of Eb on [Cl-] is established such that Eb = A + B log10[Cl-], where the value of B is typically -0.11 V per decade. The practical implications of the existence of a breakdown potential for Mg is considered in terms of the selection of an appropriate chloride ion concentration in standard corrosion tests.
published_date	2017-12-31T19:03:57Z
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score	11.04748

The influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium

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