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This study investigates the effectiveness of conversion coatings (CCs) in mitigating filiform corrosion (FFC) on acrylic-coated steel substrates, with a specific focus on iron phosphatizing and trivalent chromium conversion coatings. Aiming to evaluate the effectiveness of a simulated electrochemical approach introduced in a previous publication, several parameters are determined through an approach involving potentiodynamic polarization curves and zero resistance ammeter on bare CCs. These experiments are conducted in test solutions designed to replicate the electrolytic conditions the substrate encounters undergoing FFC. Similar measurements are collected in neutral testing solutions and the outcomes of the two approaches are discussed regarding the performances of the organic coated sample. The electrochemical evaluation of CCs highlights their potential to reduce the driving forces and nucleation tendency. However, for the steel coated with acrylic paint, while CCs reduce the initiation sites for delamination, they have limited impact on filament propagation. • Employing conversion coatings shows promise as an effective strategy to mitigate filiform corrosion on painted steel. • An electrochemical simulation approach can be applied to anticipate the performance of inorganic coatings. • Simulated quantitative data are deliberated in reference to the actual corrosion resistance. [ABSTRACT FROM AUTHOR]

Sebacate (SB) molecules were incorporated into Ca Al layered double hydroxides (CaAL-LDH) using a hydrothermal method. The resulting products underwent characterization through X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. To investigate the release kinetics and thermodynamics of the corrosion inhibitor, total organic carbon analysis (TOC) was employed. A comparison was made with CaAl-LDH prepared without corrosion inhibitors, in which nitrates were the primary anions within the layered clay structure. An assessment of anion exchange between nitrates and chlorides was conducted using total nitrogen analysis (TN). The SB anion comprised approximately 49.2% of the total dried powder synthesized, with a maximum release efficiency of around 86.7% fitting a Langmuir model. For the evaluation of the corrosion inhibition effect on steel surfaces, electrochemical impedance spectroscopy, potentiodynamic polarization, and scanning vibrating electrode technique were employed. The corrosion inhibition impact was ascribed to the liberation of SB anions from the CaAl-LDH pigments, accompanied by alkalinization stemming from partial particle dissolution. Additionally, the incorporation of organic molecules notably enhanced the stability of pigments in aqueous solutions compared to similar ones hosting nitrates. These findings suggested that CaAl-LDH pigments have potential as nanocontainers for organic inhibitors, showing promising prospects in the field of corrosion research. [Display omitted] • Synthesis of CaAl-LDHs particles with sebacate intercalated. • Sebacate anionic exchange with chlorides is efficient at 86.7%. • Organic molecule intercalation gives improved stability in water. • Steel corrosion protection is provided by chloride trapping and inhibitor release. [ABSTRACT FROM AUTHOR]

A new approach to studying the mechanism of filiform corrosion in organic coated steel based on the scanning vibrating electrode technique (SVET) and micropotentiometry (potentiometric SECM) is presented. The electrochemical activity of the process under the coating is evaluated by mapping the ionic current densities emanating from some artificial defects made in specific locations of the filament identifiable thanks to the transparency of the coating. In addition, antimony tips are employed to investigate the pH changes associated to the different corrosion reactions at the metal-paint interface. Local pH levels associated to anodic and cathodic regions are determined along the filament. [Display omitted] • Anodic and cathodic areas of filiform corrosion on organic-coated steel were identified by SVET. • The activity in the head confined into the "V-shape" morphology resulted anodic and the entire length of the tail cathodic. • Scanning micropotentiometry with an antimony microelectrode allowed local pH distributions in the filament to be measured. [ABSTRACT FROM AUTHOR]