Understanding Speciation of Lanthanum 4-Hydroxy Cinnamate and its Impact on the Corrosion Inhibition Mechanism for AS1020 Steel

Abstract

Speciation of the inhibitor lanthanum 4-hydroxy cinnamate in solution as a function of pH and concentration has been evaluated and correlated with corrosion inhibition efficiency for AS1020 steel in an aqueous chloride solution. A combination of nuclear magnetic resonance (NMR) spectroscopy, electrospray mass spectrometry (ESMS), potentiodynamic polarization, scanning electron microscopy (SEM) and profilometric techniques were found to be useful in the characterization of this system. Potentiodynamic polarization experiments established that lanthanum 4-hydroxy cinnamate inhibits well over a range of pH and concentration conditions, but more interestingly the mechanism of inhibition is dependent on the environment. It is also evident from NMR and ESMS that the species in solution are dependent on pH, and this impacts the corrosion inhibition efficiency and mechanism. These data give an insight into the types of species present in a given environment.

Rare Earth 4-Hydroxycinnamate Compounds as Carbon Dioxide Corrosion Inhibitors for Steel in Sodium Chloride Solution

“…In addition, a thinner surface film deposits on the entire steel substrate, as suggested by the EIS, XPS and SEM experiments, would account for a reduction in the cathodic kinetics (in contrast to the predominantly anodic inhibition seen in naturally-aerated systems and the addition of REM(4OHCin) 3 led to the formation of a continuous protective film on the steel surface). 26 The influence of inhibitor concentration is also consistent with this suggested mechanism, as the electrochemical results indicated improved performance, likely arising from better surface coverage with increasing amount of inhibitor. Pr(4OHCin) 3 appears to be the most efficient inhibitor under these conditions, showing the highest inhibition performance.…”

“…[25][26][27][28][29] One approach is to synthesize rare earth metal (REM) compounds with synergistic combinations of organic inhibitor molecules (rare earth organics). [25][26][27][28][29][30][31][32] It has been shown that by combining a rare earth metal with an organic ligand (such as a carboxylate) to create a multifunctional inhibitor that combines the inhibitive properties of the two components, with inhibition capability superior to that of either of the individual components at the same concentration is often observed. 25 Blin et al 25 showed some years ago that substituted rare earth organics, in particular lanthanum 4-hydroxycinnamate (La(4OHCin) 3 ), led to an enhancement in corrosion mitigation in oxygen-containing solutions.…”

“…More recently Seter et al 26 studied the speciation of rare earth organics in solution as a function of pH and concentration and showed the corrosion inhibition properties of La(4OHCin) 3 for AS1020 in 0.01 M NaCl solutions over a range of pHs. This compound was a powerful inhibitor when the pH was between 5 and 8, but was less efficient in highly acidic pH conditions.…”

Self-healing coatings

“…Pourbaix diagrams are often used as a guide for the types of deposit that might provide cathodic inhibition [128]. The deposit is usually a hydroxy-oxide, with rare earths currently of great interest [129][130][131][132][133][134][135][136][137][138]. Transition metal phosphates have traditionally been of great importance as well [139][140][141][142][143][144].…”

Metal-free coumarate based ionic liquids and poly(ionic liquid)s as corrosion inhibitors

“…These compounds can suppress both the anodic and cathodic reactions that are involved in corrosion, showing a synergistic effect between the rare earth metal and the carboxylates. [6][7][8] Among these, rare earth metal aromatic carboxylates have demonstrated the best anticorrosive performance due to the formation of a passive barrier layer that forms due to adsorption and subsequent reaction with the underlying alloy substrate. 7,9,10 From this past work, it is evident that the aromatic carboxylate, p-coumarate, provides very efficient inhibition.…”