ORALS

SESSION: CorrosionMonAM-R7	Macdonald International Symposium (Intl Sympos. on Corrosion for Sustainable Development)
Mon. 28 Nov. 2022 / Room: Andaman 2
Session Chairs: Raman Singh; Session Monitor: TBA

12:45: [CorrosionMonAM04] OS
Finite Element Analysis for Modelling Microbial and Atmospheric Thin Film Corrosion
Mohsen Saeedikhani¹ ; Daniel John Blackwood² ; ¹, Melbourne, Australia; ²National University of Singapore, Singapore, Singapore;
Paper Id: 186 [Abstract]

Thin-film corrosion is a severe issue in almost every sector. Thus, corrosion simulation under thin electrolyte films has always been of high interest as experimental studies are often challenging. For microbial corrosion, the existence of a biofilm on the metal surface impacts corrosive species' production and transportation, which is yet understood poorly. Therefore, the present corrosion models are risk-based and meant for ranking potential threats to the industrial assets, rather than trying to quantify those threats. Thus far, especially for atmospheric corrosion, progress has been made to model the effect of several essential factors on thin-film corrosion rates. Some of these parameters are electrolyte thickness, electrolyte composition, chemical reactions in the electrolyte, electrode size and change in electrode size, environmental parameters, and corrosion product deposition. However, these parameters are mainly drawn from different studies and have not been modelled concurrently in a single simulation study, making the thin film corrosion model far from being complete yet. Our research aims to resolve the problems mentioned above by employing finite element analysis using the corrosion module of COMSOL Multiphysics software. We have developed a multi-species multi-reaction moving boundary (MSMRMB) model, which not only provides flexibility for modelling altering corrosive environments but can quantify the corrosion rate. Quantification of corrosion rate will enable the industries to apply fitness for service (FFS) to the corroded pressure vessels based on the maximum pit size, operating pressure, lifetime, etc. We are aware that there is a long way to achieve a complete model, but our developed MSMRMB model is promising for this journey.

References:
[1] M. Saeedikhani and DJ. Blackwood, Corros. Mater. Degrad. 2020, 1(2), 273-281\n[2] M. Saeedikhani et al. J. Electrochem. Soc. 2020, 167, 041503\n[3] M. Saeedikhani et al. Corros. Sci. 2020, 163, 108296

SESSION: CorrosionMonPM1-R7	Macdonald International Symposium (Intl Sympos. on Corrosion for Sustainable Development)
Mon. 28 Nov. 2022 / Room: Andaman 2
Session Chairs: TBA Session Monitor: TBA

14:50: [CorrosionMonPM107] OS
Volta Potential Evolution of Aluminium Alloys under Chloride-Contaminated Thin-Film Electrolyte
Yanhan Liew¹ ; Cem Örnek² ; Jinshan Pan³ ; Dominique Thierry⁴ ; Sudesh Wijesinghe⁵ ; Daniel John Blackwood¹ ; ¹National University of Singapore, Singapore, Singapore; ²Istanbul Technical University, Istanbul, Turkey; ³KTH Royal Institute of Technology, Stockholm, Sweden; ⁴French Corrosion Institute, Brest, France; ⁵Singapore Institute of Manufacturing Technology (SIMTech), Singapore, Singapore;
Paper Id: 192 [Abstract]

Corrosion is an issue that has led to widespread cost and even danger. Thus, it is of importance to investigate the nature of corrosion initiation and/or propagation mechanisms; one such way is via analysing the nobility and electrochemical changes of the metal microstructure through their Volta potential (Ψ), which is the potential difference between a point just outside the surface of the metal and a point infinitely far away from the surface [1]. The Ψ gives information about the surface electrons, and hence can be used as a gauge of a material’s tendency towards physicochemical reactions such as corrosion [2].
Using a recently developed Scanning Kelvin Probe Force Microscopy (SKPFM) setup that incorporates an ability to vary the relative humidity [3,4], the earliest stages of localised corrosion on aluminium alloys, such as AA5083, under chloride-contaminated thin-film electrolytes were investigated at ambient temperature over the humidity range 20%-85% RH. The in-situ time-lapse SKPFM investigation elucidated magnesium silicide particle regions in AA5083, which initially showed positive Volta potential (vs matrix), suffering from severe, sharp nobility loss due to the ongoing dissolution of magnesium and the formation of rod-like corrosion products [5]. The corrosion product growth, most likely a form of nesquehonite, was highly favoured when exposed to humidities >80% RH. Transient events that occurred during the corrosion were also captured by the in-situ time-lapse SKPFM method, further demonstrating that it is necessary to measure the Volta potential during corrosion to reflect the true relationship between the Volta potential and corrosion potential or breakdown potential of a material.
Furthermore, the phenomenon of nobility adoption is discussed, detailing instances when local sites adopted the nobility of their neighbouring region. Nobility adoption seemingly occurs at elevated humidity (>80% RH) and within close proximity of a particle with large Volta potential difference relative to the matrix. Different behaviours of nobility adoption were also seen in the analysis, when the aluminium alloys were exposed to thin-film electrolyte over extended period, suggesting that the localised corrosion mechanism evolves over time.

References:
[1] J.O. Bockris, A.K.N. Reddy, M. Gamboa-Aldeco, Modern Electrochemistry 2A, Kluwer Academic Publishers, Boston, 2002. doi:10.1007/b113922.\n[2] C. Örnek, C. Leygraf, J. Pan, On the Volta potential measured by SKPFM–fundamental and practical aspects with relevance to corrosion science, Corros. Eng. Sci. Technol. 54 (2019) 185–198. doi:10.1080/1478422X.2019.1583436.\n[3] C. Örnek, C. Leygraf, J. Pan, Real-Time Corrosion Monitoring of Aluminum Alloy Using Scanning Kelvin Probe Force Microscopy, J. Electrochem. Soc. 167 (2020) 081502. doi:10.1149/1945-7111/ab8826.\n[4] C. Örnek, D.L. Engelberg, SKPFM measured Volta potential correlated with strain localisation in microstructure to understand corrosion susceptibility of cold-rolled grade 2205 duplex stainless steel, Corros. Sci. 99 (2015) 164–171. doi:10.1016/j.corsci.2015.06.035.\n[5] Y. Liew, C. Örnek, J. Pan, D. Thierry, S. Wijesinghe, D.J. Blackwood, In-Situ Time-Lapse SKPFM Investigation of Sensitized AA5083 Aluminum Alloy to Understand Localized Corrosion, J. Electrochem. Soc. 167 (2020) 141502. doi:10.1149/1945-7111/abc30d.