In Situ AFM and Electrochemical Study of a Waterborne Acrylic Composite Coating with CeO₂Nanoparticles for Corrosion Protection of Carbon Steel

Abstract

The corrosion protection of a waterborne acrylic composite coating with 1 wt% ceria nanoparticles (CeNP) coated on carbon steel in 3 wt% NaCl solution was investigated by ex-situ and in situ as well as electrochemical atomic force microscopy (AFM) observations, combined with open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. The synthesized CeNP were stabilized by acetic acid. The transmission electron microscopy characterization showed fine nano-size of as-synthesized CeNP, the ex-situ AFM imaging revealed uniform dispersion of the CeNP in the composite coating and greatly reduced nano-sized pinholes in the coating. The in situ and electrochemical (EC) AFM investigations indicate release of some CeNP and aggregates from the coating surface and then precipitation of some particles and cerium-compounds during the exposure. The OCP and EIS results demonstrated that the addition of 1 wt% CeNP leads to a significantly improved long term barrier type corrosion protection of the waterborne acrylic composite coating for carbon steel in 3 wt% NaCl solution. The beneficial effect of the CeNP is attributed to the blocking of nano-sized defects and inhibition by the cerium compounds originated from the acetic acid stabilized CeNP.Carbon steels are widely used in modern infrastructural fields, and polymer coatings are often needed for the corrosion protection. Hexavalent chromium has been extensively used for more than 60 years as anti-corrosion pigments in conversion coatings for corrosion protection. 1 However, during the last decade the use of chromatebased compounds in coatings has been highly restricted due to human health and environmental concerns, and large efforts have been devoted to develop alternatives to hexavalent chromium. Recently, the use of cerium species in conversion coatings has been explored for the corrosion protection of metals including zinc, aluminum, magnesium alloys, galvanized steel and stainless steel. Cerium-based inhibitors are becoming a promising environmentally friendly alternative to chromate used in coatings. [2][3][4] It was found that the cerium compounds reduced the rate of both the cathodic and the anodic reactions. 5,6 Waterborne-based acrylic copolymer coatings have been widely used in maintenance paints due to their excellent weatherability, hardness, water and alkali resistance. 7 These kinds of coatings are made of aqueous polymer latexes that are responsible for binding the pigments and fillers and forming a homogeneous film with good adhesion to the substrate. However, the coatings consist of acrylic-based resins and are generally not impervious to corrosive reactants such as water, oxygen and corrosive ions. 8 Their application as corrosion protection coatings for metals is limited due to the lack of permanent impenetrability, which leads to delamination and degradation of the coatings once the electrolyte solution reaches the metal-coating interface leading to corrosion of the metal. 9,10 Therefore it is necessary to develop composite ...

Carbon steel corrosion: a review of key surface properties and characterization methods

“…The in situ electrochemical study was further performed by Li et al 84 on acrylic composite coatings with CeO 2 nanoparticles for corrosion protection of carbon steel. Cerium based inhibitors are considered as green inhibitors and in situ AFM analysis revealed precipitation of the CeO 2 particles through ejection from the coating.…”

Understanding the anticorrosive protective mechanisms of modified epoxy coatings with improved barrier, active and self-healing functionalities: EIS and spectroscopic techniques

“…This approach advances numerous benefits over direct additions such as (a) eliminates the undesirable interaction of active agents with the coating constituents, (b) enhances the even distribution of low soluble active agents in the coating matrix, and (c) reduces the leaching rate of high soluble active agents in aqueous systems 9 – 13 . Consequently, in this regard, several types of nano / micro containers have been introduced for the encapsulation of active agents, such as the inorganic non-metallic oxides (SiO 2 , silica particles, clays) 14 – 16 , metallic oxides (Mn 2 O 3 , CeO 2 ) 17 , 18 , carbon nanoparticles (carbon nanotubes) 19 – 21 , and organic nano / micro-containers (polyelectrolytes, polymer shells) 16 , 22 – 24 . Regrettably, the industrial application of some of these nano/micro containers is confronted by some setbacks.…”

“…To better understand the protective mechanisms of our innovative coatings, and to provide evidence for potential application, long-time impedance spectroscopy technique (EIS) supported with scanning electron spectroscopic technique (SEM) were adopted. These complementary techniques were selected based on the fact that, previously, most active and self-healing protective coatings researchers employed a short-term electrochemical test methods 2 , 9 – 18 , which is not sufficient enough to predict the possible long-term protective ability of the coatings when deployed in service; and does not provide mechanistic insights into the long-term combined active, passive and self-healing protective actions. In this regard, we approximated the experimental conditions to real field situation by applying a coating thickness of ~200μm and extending the experimental time till significant weak protection is recorded.…”

Self-assembly of plant protein fibrils interacting with superparamagnetic iron oxide nanoparticles

“…It should be kept in mind that because MFM is sensitive to the strength and polarity of near-surface stray fields produced by ferromagnetic domains, rather than to the magnetization itself, it is not straightforward to deduce the overall domain topology from an MFM image. The statistical data was analyzed using Nanoscope analysis for flattening (1 st order) and calculation of magnetic phase shift and Gwyddion for statistical analysis 78 .…”