Abstract
Corrosion protection for carbon steel by three waterborne styrene-acrylic latex coatings with different glass transition temperature (Tg) and levels of hydrophobicity has been studied by in-situ atomic force microscope (AFM) and electrochemical impedance spectroscopy (EIS) measurements in 3.0 wt% NaCl solution. The AFM images reveal the micro- and nano-structure of and pinholes in the coatings as well as their changes during exposure in the solution, whereas the EIS spectra vs. time of exposure show the barrier property, stability and degradation of the coatings. The coating with crosslinking and high level of hydrophobicity exhibited a high barrier property and long-term corrosion protection in the solution despite of some shallow pinholes. The coating without crosslinking but having high Tg and high level of hydrophobicity also displayed a high barrier property and certain stability although initial changes occur in the solution. However, for the coating without crosslinking and with low Tg and relative low level of hydrophobicity, some dissolution and open-up of defects occurred on the surface shortly after exposure and the coating lost its barrier property rapidly in the solution. The reasons for the different behaviors between the coatings are discussed with respect to the crosslinking, Tg and the hydrophobicity level of the coating.
Highlights
In-Situ atomic force microscope (AFM) and electrochemical impedance spectroscopy (EIS) Study of Waterborne Acrylic Latex Coatings for Corrosion Protection of Carbon Steel
Waterborne acrylic coatings are based on aqueous acrylic latexes that are responsible for binding the pigments and fillers and forming polymer films with good adhesion to the substrate
A high Tg favors the mechanical properties of the film as long as an appropriate chain interdiffusion is achieved, usually by adding plasticizers that will evaporate during the film formation process.[14]
Summary
Functional monomers Crosslinking system Solid content (%) 1h at 1059◦C ISO 3251 Particle size (nm) ISO 13321 pH ISO 976 Tg◦C (DSC). Prior to the in-situ measurements, AFM images of the coatings in the dry condition were obtained for comparison. The in-situ AFM imaging was performed repeatedly in pure water (Milli-Q, resistivity 18.2 M cm) and 3.0 wt% NaCl solution, respectively, after different exposure times, in some cases up to 100 hours. Root mean square roughness (Rq) is the average of the measured height deviations taken within the evaluation length and measured from the mean line and it is calculated as: Rq =. The exposed sample area was 10 cm[2], and the EIS spectra were acquired at the open-circuit potential, with ac perturbation amplitude of 20 mV and the frequency range 105 Hz to 10−2 Hz. The EIS measurements were performed at room temperature and repeated at least three times
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