Effect of 1-Hydroxyethylidene-1, 1-Diphosphonic Acid on the Corrosion of SS 41 Steel⁽¹⁾ in 0.3% Sodium Chloride Solution

The effectiveness of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) as a corrosion inhibitor was investigated by measuring corrosion weight losses and polarization curves of SS 41 steel in 0.3% NaCl. In concentrations lower than 50 ppm of HEDP, the corrosion of SS 41 steel was inhibited in accordance with the Langmuir adsorption isotherm of HEDP on the steel. The adsorption was believed to be a chemical adsorption resulting from the value of adsorption heat. In concentrations greater than 50 ppm of HEDP, the iron complex of HEDP developed, and the inhibition effect was decreased. Instead, it caused rust to be removed from the steel surface. The mutual inhibition effect by adding both HEDP and the Zn²⁺ ion in 0.3% NaCl solution was progressively more increased. It was shown that HEDP does not easily decompose.