Aminotris(Methylenephosphonic acid) and sodium gluconate as inhibitors of carbon steel corrosion in 3.5% NaCl solution

Abstract

Corrosion inhibition of carbon steel (RSt 37-2) protected by mixtures of aminotris (methylenephosphonic acid) (ATMP) and sodium gluconate (SG) in 3.5% NaCl solution has been studied. The effect of combined action of ATMP and SG has been evaluated using Tafel polarization and microscopy techniques. SG and ATMP were added in low concentrations. Concentration range of SG was from 1 mM to 10 mM, and ATMP was added in concentrations from 1 to 6 mM (mmol ‧ L–1). As control experiment, corrosion inhibition efficiencies of SG and ATMP on carbon steel corrosion in 3.5% NaCl were separately evaluated in one inhibitor system. Afterwards, inhibitors were employed in mixtures (two inhibitors system). In both experiments the majority of employed inhibitor concentrations significantly decreased corrosion current. When employed alone both inhibitors were more susceptible to pitting corrosion or excessive oxidation product formation. When employed in mixtures some inhibitor combinations, primarily those that were composed of moderate concentrations of both inhibitors, exhibited excellent general and pitting corrosion inhibition. When using SG as only inhibitor anodic inhibition mechanism was observed, whereas ATMP alone acted as cathodic inhibitor. Using both inhibitors predominant mechanism of cathodic inhibition was observed. The results clearly showed that carefully selected mixtures of ATMP and SG could successfully inhibit corrosion of carbon steel in 3.5% NaCl solution.