BEHAVIOR OF ASPARTIC-ACID AS A CORROSION-INHIBITOR FOR STEEL

Corrosion inhibition of steel by aspartic acid (C4H7NO4), an amino aci d of low molecular weight, was found to depend strongly on pH. At a pH less than the ionization constant at similar to 9.5 to 10 (measured a t 25 degrees C), C4H7NO4 appeared to accelerate corrosion. Above that pH, it acted as a corrosion inhibitor for steel. A specially construct ed potential-pH diagram for iron (Fe) that incorporated C4H7NO4 showed the change in behavior was accompanied by the most stable thermodynam ic state changing from an iron aspartate complex to iron oxide. Polyme rized C4H7NO4 (polyaspartic acid) behaved in a similar manner. Some ot her amino acids of low molecular weight behaved similarly.