In Situ Investigation of Migration of Cations during Electrolyte Spreading on Chromium Coated Steels Electrodeposited from Trivalent-Chromium Electrolyte

Abstract

Resistance to corrosion and inhibition of cathodic delamination of polymer topcoat makes chromium coated steels suitable for application in the packaging industry. These coatings were traditionally produced from hexavalent chromium electrolytes. These coatings are now being phased out due to the carcinogenic nature of hexavalent chromium used in the production process (by the REACH regulation in the European Union). Electrodeposition from trivalent chromium containing electrolyte is being considered as an alternative to replace these traditional hexavalent-chromium coated steels. The cathodic delamination behavior of polymer topcoat on these trivalent-chromium coated steels were studied in detail previously [1-3]. However, the factors that result in inhibition of cathodic delamination are still not well understood.The two important factors influencing the rate of cathodic delamination are the electron transport and cation migration on the surface. The aim of this study is to understand the influence of complex composition of these trivalent-chromium coatings on the electrical conductivity and ion migration on the surface of the coating at the microscopic scale. The electronic conductivity of the coatings was studied using current-sensing atomic force microscopy to understand electron transfer occurring at the cathodic delamination front. Cation migration during oxygen-reduction induced spreading of electrolyte on these trivalent-chromium coated steel was studied using in situ scanning Kelvin probe force microscopy. The coatings are found to highly resist electron transport. Heterogeneities observed in the microscopic scale using the current-sensing atomic force microscope are correlated to the behavior observed during electrolyte spreading. The kinetics of spreading observed at microscopic scales are similar to that observed using a scanning Kelvin probe at larger scales. The results demonstrate in situ scanning Kelvin probe force microscopy as an effective tool to study the migration of cations during electrolyte spreading and the local heterogeneities at the microscopic scale. Warren, David & N. McMurray, H & de Vooys, Arnoud. (2013). Localised SKP Studies of Cathodic Disbondment on Chromium/Chromium Oxide Coated Steel. ECS Transactions. 50. 67-78.Wint, N & de Vooys, Arnoud & Mcmurray, Hamilton. (2016). The corrosion of chromium based coatings for packaging steel. Electrochimica Acta. 203. 326-336.James E. Edy, Hamilton N. McMurray, Koen R. Lammers, Arnoud C.A. deVooys (2019). Kinetics of corrosion-driven cathodic disbondment on organic coated trivalent chromium metal-oxide-carbide coatings on steel. Corrosion Science. 157. 51-61.