Corrosion Protection in Chloride Environments of Nanosilica Containing Epoxy Powder Coatings with Defects

Abstract

This paper describes the use of innovative, nanosilica containing epoxy powder coatings for the corrosion protection of steel. Two types of nanosilica particles (hydrophilic -HL-and hydrophobic -HB-) were mixed by ball milling with the powders (0.75 wt.%). The adequate homogeneity and embedding of nanoparticles were verified by transmission electron microscopy.The corrosion performance of the coatings as-received, and with HL and HB additions, were analyzed in 3.5 wt.% NaCl solutions. The mechanism and rate of delamination of defective coatings under drops simulating atmospheric conditions were analyzed by Scanning Kelvin Probe measurements for 30 days. The results show that the corrosion attack progresses through a cathodic delamination mechanism. Besides, fully-immersed samples, with and without defects, were monitored by electrochemical impedance spectroscopy. In defective coatings under these conditions, the occurrence of anodic undermining is proved. The results obtained reveal that the corrosion driven coating failure is delayed in the case of the epoxy coatings containing nanosilica. This delay is larger in the case of HB additions than HL additions in both atmospheric and immersion conditions. The corrosion mechanism observed is dependent upon exposure conditions. It is proposed that the nanoparticles delay water absorption, thus delaying corrosion attack.

Effect of additions of anticorrosive pigments on the cathodic delamination and wear resistance of an epoxy powder coating

“…Different studies are found in the literature regarding improvement of protection given by the coatings to the metal substrates in aggressive environments. Some work has been able to obtain mechanical improvements in coatings with different types of inert reinforcements [6,7]. At the same time, other authors have focused more on manufacturing anticorrosive coatings with the addition of smart corrosion inhibitors that present different protection mechanisms when the corrosive agents appear.…”

“…Moreover, it has been recently reported that mesoporous nanosilica particles can exert an inhibitory effect against delamination [10]. As far as nanoparticles are concerned, their direct effect in metalcoating adhesion improvement and polymer crosslinking cannot be ignored [6], as well as the improvement of strength and barrier properties of coating [10]. However, the use of nanosilica as smart carriers for corrosion protection has been strongly developed in recent years, acting as reservoir for functional species (inhibitor/self-healing agent).…”

“…SKP allows the delamination mechanism of the painted system to be understood, once a defect has been previously made in the coating, and the damage progresses under drops or ultra-thin electrolyte layers [27]. Moreover, using SKP, it can be obtained information about the delamination rate and how it evolves with time [6], and also identify the rate-determining step of the mechanism [28]. Though many studies have been published with interesting results using SKP in liquid organic coating systems [17,29,30], there is currently only one that examines the progress of the delamination front of powder coatings using this technique [6].…”

Electrochemical study on using aminated MIL–101(Cr) as corrosion inhibitor for mild steel in acidic environment

“…Organic inhibitors are one contemporary method for protecting metals against acidic, neutral and basic corrosion. Different organic materials, mainly those rich in oxygen, sulfur and nitrogen heteroatoms, have been selected as a good strategy for protecting MS in a wide variety of acidic environments, including hostile chloride ions (Mazumder et al , 2014; Zou et al , 2014; Bouanis et al , 2016; Zuo et al , 2017; Fernández-Álvarez et al , 2020; Xia et al , 2021). In acidic medium, the positive charge of steel surface allows for either direct coordination with the electronegative functional moieties of organic inhibitors or indirect adsorption of inhibitor cations species to form self-assembled layers via a synergistic effect with chloride ions that improve anticorrosion property (Mazumder et al , 2014; Elshakre et al , 2017; Li et al , 2017).…”

Influence of Microdefect Size on Corrosion Behavior of Epoxy-Coated Rebar for Application in Seawater-Mixed Concrete

“…Corrosion behavior and mechanisms of defective coated steel have been studied extensively. Fernández-Álvarez et al [8] proposed that the corrosion proceeds by anodic undermining when defective coatings are immersed in 3.5 wt.% NaCl solutions. As the reaction proceeds, oxygen is consumed in cathodic reduction, and corrosion products form in the defect, hindering the transportation of dissolved oxygen.…”