Comparison of electrochemical impedance spectroscopy and electrochemical noise measurement of plasma polymerised films as pretreatment for cold rolled steel

Plasma polymerised films have shown promise as possible alternatives to phosphating for the corrosion protection of cold rolled steel. After plasma cleaning using either a mixture of argon and hydrogen or a sequential combination of argon and hydrogen followed by oxygen steel panels were coated with a 250 nm thickness plasma polymerised film of dimethylsilane followed by 30 mum of cathodic electrocoat. Various plasma cleaning conditions were compared, and both electrochemical impedance spectroscopy and electrochemical noise measurement were used to rank the performance of the system. Results from the two types of test correlate reasonably showing that the system is fairly effective in protecting the substrate from the onset of corrosion. These preliminary results demonstrate that plasma cleaning is a very important step in the process. (C) 2000 IoM Communications Ltd.