INHIBITION OF IRON CORROSION BY COMPLEXONATES OF ETHYLIDENEDIAMINOTETRAMETHYLENEPHOSPHONATES

The protection of low-carbon steel with ethylenediaminotetramethylenep hosphonic acid (EDTP) and its complexes with bivalent metals in soft w ater (30 mg/l NaCl and 70 mg/l Na2SO4) was studied. It was demonstrate d that the complexone itself is close in its protective ability to hyd roxyethylidenediphosphonic acid (HEDP), but its complexes with Mg, Ca, and especially with Co are better than the corresponding hydroxyethyl idenediphosphonates. Depending on the solubility of the hydroxide of a metal acting as a complexing agent, the protective ability of the com plexes has a maximum. The decrease in inhibitor efficiency when the co mposition varies, including zinc complexes of different phosphonic aci ds, is due to an increase in complexonate stability hindering the form ation of a protective film of poorly soluble Me(OH)(2) on the electrod e. The influence of the inhibitors under discussion on the kinetics of electrochemical reactions, which cause iron corrosion in neutral aque ous solutions, was analyzed.