Hexafluorozirconic acid based surface pretreatments: Characterization and performance assessment

Environmentally Friendly Anticorrosive Polymeric Coatings

This paper provides a synthetic and comprehensive overview on environmentally friendly anticorrosive polymeric coatings. Firstly, the economic and environmental impact of corrosion is presented to highlight the need of anticorrosive polymeric coatings as a flexible and effective solution to protect a metal. Secondly, the implementation of regulations together with the consumer awareness for environmental considerations and protection of health are the driving force for a progressive but significant change in the sector. Therefore, within the protective organic coatings market, this article provides a review of the most recent developments in environmentally friendly solutions, including bio-based and water-borne epoxy, hyperbranched polyester for low- volatile organic compounds (VOC) coatings, waterborne polyurethane and non-isocyanate polyurethanes (NIPUs), and graphene or bio-based fillers for acrylics. Moreover, this paper outlines new trends such as smart additives, bio-based corrosion inhibitors, and functional antibiocorrosive coatings as superhydrophobics. Finally, industrially relevant applications of environmentally friendly anticorrosive polymeric coatings including solutions for marine and off-shore industries are summarized.

Green Nanocoatings Based on the Deposition of Zirconium Oxide: The Role of the Substrate

Herein, the influence of the substrate in the formation of zirconium oxide monolayer, from an aqueous hexafluorozirconic acid solution, by chemical conversion and by electro-assisted deposition, has been approached. The nanoscale dimensions of the ZrO₂ film is affected by the substrate nature and roughness. This study evidenced that the mechanism of Zr-EAD is dependent on the potential applied and on the substrate composition, whereas conversion coating is uniquely dependent on the adsorption reaction time. The zirconium oxide based nanofilms were more homogenous in AA2024 substrates if compared to pure Al grade (AA1100). It was justified by the high content of Cu alloying element present in the grain boundaries of the latter. Such intermetallic active sites favor the obtaining of ZrO₂ films, as demonstrated by XPS and AFM results. From a mechanistic point of view, the electrochemical reactions take place simultaneously with the conventional chemical conversion process driven by ions diffusion. Such findings will bring new perspectives for the generation of controlled oxide coatings in modified electrodes used, as for example, in the construction of battery cells; in automotive and in aerospace industries, to replace micrometric layers of zinc phosphate by light-weight zirconium oxide nanometric ones. This study is particularly addressed for the reduction of industrial waste by applying green bath solutions without the need of auxiliary compounds and using lightweight ceramic materials.

Unraveling the Formation Mechanism of a Hybrid Zr-Based Chemical Conversion Coating with Organic and Copper Compounds for Corrosion Inhibition

Environmentally friendly chromate-free, zirconium (Zr)-based conversion coating is a promising green technology for corrosion protection. Additives in the surface treatment provide critical functionalities and performance improvements; however, mechanistic understanding as to how the additives influence the coatings remains unclear. In this study, a new organic-inorganic hybrid Zr-based conversion coating combines copper (Cu) compounds and polyamidoamine (PAMAM), taking advantage of the complementary nature of organic and inorganic additives. A multimodal approach combining electron and X-ray characterization is applied to study the interaction of Cu²⁺ and PAMAM and the resulting impacts on coating formation. Adding PAMAM changed the surface morphology, thickness, distribution of Cu in the clusters, and void formation of the coatings. High PAMAM (100-200 ppm) leads to little conversion coating formation, and low PAMAM (0-25 ppm) shows voids formation under the coatings. Moreover, PAMAM incorporates in the coating in the form of a PAMAM-Cu complex with a higher concentration toward the surface, providing an organic layer at the surface of the coating. X-ray absorption near-edge structure (XANES) spectroscopy shows the difference between the conventional and the hybrid coating treatments in an alkaline solution to simulate the E-coat process, suggesting the contribution of PAMAM in the enhanced chemical stability in an alkaline environment. Therefore, an intermediate range of addition of PAMAM (50 ppm) is optimal to (1) avoid excessive voids formation, (2) promote some Cu cluster formation and thus enhance the Zr-based coating formation, and (3) incorporate organic components into the coating to improve the adhesion of the subsequent coatings. Overall, this work furthers our knowledge on the formation mechanism of an effective and environmentally friendly hybrid conversion coating for corrosion inhibition, demonstrating a critical processing-structure-property relationship. This study will benefit future development of green and effective surface treatment technology.

Pretreatment with a β-Cyclodextrin-Corrosion Inhibitor Complex Stops an Initiated Corrosion Process on Zinc

Metal pretreatment is typically the first step in a reliable corrosion protection system. This work explores the incorporation of complexes between the cyclic oligosaccharide β-cyclodextrin (β-CD) and the molecular organic corrosion inhibitor 2-mercaptobenzothiazole (MBT) into an oxide-based pretreatment layer on metallic zinc. The layers were produced by a precorrosion step in the presence of β-CD. The resulting films have a morphology dominated by spherical particles. X-ray photoelectron spectroscopy investigations of the surfaces show the sulfur atoms of MBT to be partially oxidized but mostly intact. Samples pretreated with such a layer were subsequently coated with a model polymer coating, and the delamination of this model coating from an artificial defect was monitored by a scanning Kelvin probe (SKP). The SKP results show a slow down of delamination after several hours of the ongoing corrosion process for surfaces pretreated with the complexes. Finally, an increase in the electrode potential in the defect was observed, with a subsequent complete stop in delamination and repassivation of the defect after ≈10 h. This repassivation is attributed to the release of MBT after the initiation of the corrosion process. Most likely, the increase of pH, combined with the availability of aqueous solution, facilitates the MBT release after the initiation of a corrosion process. Consequently, complexes formed from β-CD and corrosion inhibitors can be effectively incorporated into inorganic pretreatments, and the inhibitor component can be released upon start of the corrosion process.

Nanostructured vanadium-based conversion treatment of mild steel substrate: formation process via noise measurement, surface analysis and anti-corrosion behavior

The bath pH, vanadia solution concentration and immersion time were optimized for the chemical surface treatment of ST12 mild steel by vanadium-based conversion coating (VCC). Nano-sized vanadium oxide/hydroxide particles were found to form on the steel surface.