MECHANISM OF CORROSION INHIBITION OF MILD -STEEL BY GALLIC ACID IN ALKALINE-SOLUTION (PH=11)

Corrosion inhibition behaviors of gallic acid against mild steel under alkaline conditions were investigated by physico-chemical methods and corrosion tests. Experimental results have indicated that gallic acid acts as an oxygen scavenger and also a passivation type-corrosion inh ibitor. The following three mechanisms were considered for the role of gallic acid in the passivation process; i) encouragement of passive f ilm formation based on Fe3+-gallic acid complexes, ii) formation of a passive film by H2O2 generated in the gallic acid-O2 reaction, and iii ) promotion of passive film formation based on Fe (OH)3 reduction (Sch ikorr reaction). It is concluded from experimental results, that mecha nism iii) is most likely.