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.

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Chemical inhibitors are widely used to protect metallic alloys from corrosion in aqueous environments. This Letter investigates the possible synergistic behavior of a quaternary ammonium carboxylate compound toward the development of a new system taking advantage of the surface activity of a known antimicrobial surfactant molecule, hexadecyl trimethylammonium cation, combined with a known organic corrosion inhibitor, the trans-4-hydroxy-cinnamate anion. Short-term potentiodynamic polarization (PP) studies combined with immersion in aqueous chloride solutions demonstrated the high inhibition efficiency of the combination of ions, and NMR pfg-diffusion measurements revealed micellar formation that was concentration- and pH-dependent. The NMR data suggest that speciation changes occur in the solution that correlate with enhanced corrosion inhibition efficiency at higher pH and at concentrations above the CMC of the compound. This new contribution may provide a rational molecular design toward delivering corrosion inhibitors to a metal surface through controlled speciation in solution.

The commercially available high strength steel, HY80, has been commonly used as part of naval hull construction since the 1950s. Corrosion of HY80 is associated with high costs due to material replacement, labour and lengthy down times of assets. The use of corrosion inhibitors as part of the steel paint system is a cost-effective method of stifling corrosion attack. Incorporation of an antimicrobial component into the inhibitor is also beneficial in combatting microbiologically influenced corrosion (MIC). This work examines the efficacy and mechanisms of corrosion inhibition from mixing lanthanum trans−4-hydroxy cinnamate (La(4OHCin) 3 ) with the candidate antimicrobial compounds, imidazolinium trans−4-hydroxy cinnamate (IMI-4OHCin) or cetrimonium nalidixate (CetNal) in artificial seawater. The most effective inhibitor combination was the mixture of La(4OHCin) 3 and IMI-4OHCin at their respective solubility limits (La+IMI). Examination of steel surfaces with optical profilometry after a 5 day immersion period concluded that the presence of La+IMI in solution resulted in significant minimisation of material corroded from the steel relative to the uninhibited sample. The inhibition mechanism for this mixture was determined to be predominantly anodic. On the other hand, all solutions containing the CetNal compound appeared to accelerate corrosion attack.

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<p><a></a>High strength steel in marine environments suffers from severe corrosion susceptibility and the presence of bacteria can exacerbate the effect, accelerating degradation via microbiologically influenced corrosion (MIC). Here we propose a novel approach to MIC inhibition by designing a system capable of limiting the effects of both bacteria growth and corrosion. The combination of a newly synthesised compound, cetrimonium 4-hydroxycinnamate, with lanthanum 4-hydroxycinnamate was the only system tested to date that could both inhibit abiotic corrosion in artificial seawater and minimise bacteria consortium densities over an exposure period of 24 hours. </p> <p>The electrochemical data for the La+Cet mixture demonstrated the significant inhibition of both abiotic corrosion to a level similar to La(4OHCin)₃, as well as the ability to reduce bacteria densities of single strains and a consortium. This is unlike the La+CetNal mixture which accelerated abiotic corrosion and the La+IMI which had an insignificant effect on microbial densities (Catubig et al. 2020). </p> <p>A compatible mixture of ionic inhibitors was achieved by using the same cinnamate anion. </p> <p>This mixture of Cet-4OHCin and La(4OHCin)₃ demonstrated significant abiotic corrosion inhibition and bacteria density reductions, making it a strong candidate as an MIC inhibitor system for 80HLES. </p> <p>The Cet-4OHCin compound and its mixture with La(4OHCin)₃ retained relatively low sensitivity towards skin and intestinal cells, making it a safer and more attractive alternative than other more hazardous corrosion inhibitor materials. </p>

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