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Corrosion of metals by acidic beverages

2003

Hi,

I'm doing my thesis on corrosion of wires (one of them Stainless steel 304/316) in phosphoric acid and citric acid based beverages (pH of 2.4 and 3.3 respectively) using anodic polarization with SCE at 10 mv/15 seconds and comparing them to corrosion behaviour in artificial saliva (NaSO4,KCl, urea. In preliminary investigations the breakdown potential of SS in artificial saliva was noted at 500 mv approx. with a sudden rise in current density. In phosphoric acid based beverages, the current density increased steadily up to 900 mv followed by a decrease in current density up to 1200 mv followed by a sudden increase in current density. I was expecting the breakdown potential to be reached earlier in case of acid based drinks (low pH,carbonic acid, aerated, acid based). I presume that phosphoric acid could have a mild passivating effect on SS, please give your opinions regarding this particular behaviour and what to make of it.

Thanks,

Anup Holla
post graduate student - Mangalore, Karnataka, India