Zinc-Layered Hydroxide Salt Intercalated with Molybdate Anions as a New Smart Nanocontainer for Active Corrosion Protection of Carbon Steel

Abstract

The use of smart nanocontainers to store corrosion inhibitors in coatings significantly increases the efficiency and durability of the coating, providing active corrosion protection.Here we report the synthesis of a zinc-layered hydroxide salt (LHS) and its use as a novel nanocontainer for this purpose, storing the corrosion inhibitor molybdate in the interlayer region of the LHS. Layered zinc hydroxide molybdate (ZHM) was obtained by anion-exchange reactions using layered zinc hydroxide acetate (ZHA) as a precursor, obtained by alkaline coprecipitation. The release behavior of molybdate from the ZHM nanocontainers in aqueous NaCl solution (0.05 mol/L) was evaluated using UV− vis absorption spectroscopy. The molybdate release from the ZHM nanocontainers was realized by the anion-exchange mechanism, where chloride anions replaced intercalated molybdate anions. The release was fast in the first minutes of exposure, followed by a controlled release afterward, reaching about 35% of cumulative amount of released molybdate after 30 days of exposure. The anticorrosion effect provided by the ZHM nanocontainers for carbon steel was investigated by electrochemical impedance spectroscopy. The steel substrate was coated with an epoxy resin loaded with ZHM nanocontainers (5 wt %) and immersed in an NaCl solution (0.05 mol/L) to evaluate the active mechanisms of inhibition and the anticorrosion properties of the loaded coating in comparison with a neat coating (blank). The coating loaded with ZHM nanocontainers presented the best corrosion protection performance, exhibiting an increase of R C (coating resistance) with the immersion time and superior R P (polarization resistance) for all the measured periods, compared to the blank. This effect is a consequence of the double mechanism of protection provided by the ZHM nanocontainers: (i) stimulus-response release of molybdate and its active inhibition in the scratched region by the formation of an insoluble protective film, simultaneously with (ii) removal of the corrosive chloride species from the medium.

Improved Interfacial Interactions of Dip Coatings by In Situ Introducing Silica to Enhance Corrosion Resistance and Metal Bonding Strength

“…R p is generally used as a quantitative indicator of the barrier properties of a coating. Because of the dielectric nature of epoxy-based coatings, an extra constant phase element (CPE c ) is introduced into the circuit. − The capacitive loop, which is caused by electric double-layer capacitance and interfacial charge transfer processes, is represented by the semicircle in the Nyquist plots. In general, the R s , R ct , and coating resistance against ion transfer ( R p ) can be determined by locating the impedance intercept of the Nyquist plot from high frequency to low frequency with respect to the real axis.…”

Double Stimuli-Responsive Conducting Polypyrrole Nanocapsules for Corrosion-Resistant Epoxy Coatings

“…Various nanocontainers with different reservoirs and stimuli-responsive mechanisms have been developed for corrosion protection. Examples are polyurea microcapsules loaded with 2-mercaptobenzothiazole, multisubstituted triazole delivered from a metal-organic framework, TiO 2 nanotubes encapsulating dodecylamine, zinc-layered hydroxides intercalating molybdate anions, calcium carbonate particles loaded with triethanolamine and polyethyleneimine, and mesoporous silica nanoparticles loaded with sodium phosphomolybdate . These stimuli-responsive nanocontainers actively protect their metal substrates by sensing the changes in physical or chemical signals (such as pH, temperature, local defects, and humidity) during the corrosion process.…”

Direct Growth of Hexagonal Boron Nitride Nanofilms on Stainless Steel for Corrosion Protection

“…Therefore, the effective protection of stainless steel from corrosion is of extreme importance. Current strategies applied to enhance corrosion resistance are mainly based on barrier coatings that separate steel surfaces from the corrosive environment and consequently inhibit chemical reactions. , Various materials, such as inert metals, conductive polymers, − ceramics, , and smart nanocontainers with inhibitors, have been utilized as protective layers introduced onto the targeting surfaces. In spite of their excellent anticorrosive performance, it still remains challenging for these coatings to provide long-term protection in a harsh environment, such as ambient condition, elevated temperature, and humidity, which would severely restrict their application scenarios.…”