EIS study of blister formation on coated galvanised steel in oxidising alkaline solutions

• Blistering of polymer coated galvanised steel was studied in saline oxidising media.
• EIS was used to monitor blister initiation and growth.
• Ionic species are both, initiating and supporting blister growth.
• Investigations quantify the influence of temperature and salt concentration.

The performance of polymer coated galvanised steel sheet in alkaline solutions with and without saline components containing sodium percarbonate as an oxidising agent was investigated by visual inspection, light microscopy and electrochemical impedance spectroscopy (EIS). It was found that ionic species are both, they are necessary to initiate blistering, but also support blister growth. Sodium percarbonate accelerates blister growth. Detailed investigations concerning the effect of temperature and salt concentration were made. Blister growth kinetics was followed by EIS and is in good agreement with visual inspection.