Effects of Corrosion Inhibiting Pigment Lanthanum 4-Hydroxy Cinnamate on the Filiform Corrosion of Coated Steel

Abstract

Corrosion protection by lanthanum hydroxy cinnamate (La(4OH-cin) 3 ) in a polyurethane based varnish coating for mild steel has been investigated. Filiform scribe tests, energy-dispersive X-ray spectroscopy (EDXS) and potentiodynamic polarisation (PP) techniques have been powerful tools to better understand the corrosion process at defects and under the coating. Filiform scribe tests showed that La(4OH-cin) 3 , as a pigment in a coating, inhibited the initiation and propagation of both delamination and filiform corrosion (FFC) on coated steel. The PP experiments provided an insight into the fundamental mechanism of FFC. The results suggest that La(4OH-cin) 3 behaves as a mixed inhibitor and stifles the initiation and propagation of FFC. In this paper, the theory of delamination leading to FFC and the likely mechanism of inhibition by the La(4OH-cin) 3 will be discussed.

Filiform corrosion as a pressure-driven delamination process

“…The precise mechanism by which filiform corrosion propagates on organic coated metals is still under debate. Various possible processes have been proposed as the primary cause for the propagation, including anodic undermining, 2,8,9 cathodic delamination [10][11][12] and mechanical delamination through (electro)osmotic forces. 2,13 The evolution of the various proposed ideas can be found elsewhere.…”

Cation Effect in the Corrosion Inhibition Properties of Coumarate Ionic Liquids and Acrylic UV-Coatings

“…Moreover, the potentiodynamic polarization results also show significant current fluctuations. Those fluctuations refer with metastable pitting, in which there is a constant breakdown and repair of a passive film [1,2]. In most cases, the corrosion current decreased considerably compared with the control, yielding very high inhibitor efficiency values.…”

“…Materials deterioration by corrosion is one of the biggest technological issues nowadays causing significant economic losses [1]. Corrosion can be seen in our daily life in packaging, pipelines, infrastructure, and in chemical industries [2].…”

“…Among the different ionic compounds, 2-methylimidazolinium p-coumarate was shown to be a most effective inhibitor, showing a strong anodic inhibition effect [13][14][15][16][17]. The p-coumarate anion has also been shown to be effective when coupled to various other cations, including rare earth metals [1,9,17].…”

Design of Polymeric Corrosion Inhibitors Based on Ionic Coumarate Groups

“… 1 This material deterioration generates significant financial losses every year. 2 Corrosion can be found everywhere, on food cans, pipelines, bridges, and other structures. 3 For this reason, corrosion inhibitors, which suppress the anodic and/or cathodic electrochemical reaction, present in corrosion were developed in the last century.…”