Rust layer growth and modification by a tannin-based mixture for lowering steel corrosion rates in neutral saline solution

Abstract

Concomitant rust growth on a rust-free surface and conversion by a solution of tannin, propolis and benzoate has been investigated in the present study with the aim of producing a modified rust layer, more resilient and protective than a pure rust layer. Under such circumstances, balancing simultaneous but contradictory processes of corrosion acceleration by iron chelation and corrosion inhibition by ferric tannate precipitation is crucial for layer formation. Benzoate served as an iron corrosion inhibitor in the layer formation stage while the propolis added to the tannin solution improved the modified rust layer protective efficiency. Corrosion rates lower than 5 mpy that are acceptable from the practical viewpoint are attained with the inhibitor-modified rust layer, both, in quiescent solution and up to a linear velocity of the solution approximately equal to 1.5 m s⁻¹.

GRAPHICAL ABSTRACT