I would like to make a short experiment, which is easy to setup to demonstrate electrochemical investigation of corrosion by a potentiostat.
I was thinking of a polarization curve.
An experiment that can be performed without any dedicated corrosion equipment is preferred.
If you have a protocol or documentation describing such an experiment, I would appreciate it, if you can share it.
Hi, I think mild (unalloyed) steel in simple tap water solution would be pretty easy. Just wait for some minutes for a relatively stable OCP (it will drop to negative potentials within some minutes), then polarize from -250 to +250 mV from the last measured OCP, which should be about -550 mV vs. sat. Ag/AgCl. Expect to get 20 to 50 µA/cm² of corrosion current density after tafel evaluation.
Another experiment would be to use simple stainless steel (passive) in neutral solution with about 5.8 g/L NaCl (which is about 0,1 M). Measure again the OCP and start -100 mV from that and polarize in anodic direction up to 1000 mV or 100 µ/Acm² (as a termination or reverse criterion). You can expect increasing current at a (critical/pitting) potential of about 300-400 mV vs. sat. Ag/AgCl.
If you dont have the materials, look in your kitchen. Non-magnetic stainless materials are mostly 304 SS (18Cr 10Ni). Or look in your workshop for nails, these are most likely mild steel (they rust). Use some kind of inert metallic material (or carbon) as a counter electrode (larger in area than working electrode). Finding a stable reference, on the other hand, is not so easy. You can try silver wire, which may form some AgCl on its surface if put in a solution with high chloride content and applied anodic potentials/current for some minutes. Then it will form a relatively stable potential in a 0.1 M NaCl solution of about 295 mV vs. NHE (or 96 mV vs. sat. Ag/AgCl).
Good luck and have fun ;-)
Andreas
(owner of a PalmSens4 by the way ;-)
I forgot to mention, use 1 to 5 mV/s polarization speed (for demo experiments) and a working electrode area of about 1 to max. 10 cm² (since Palmsens is a little bit limited with high currents ;-)
Thank you, Andreas.
Usually, people don't have mild steel lying around, do they?
I tried a paper clip which I had treated with sand paper, but for some reason the OCP and the Corrosion potential where pretty far away from each other. Is there a household item or something in an electronics workshop, which could be easily transformed into a sample?
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