Corrosion investigation of new hybrid organic/inorganic coatings for carbon steel substrates: Electrochemical and surface characterizations

This work examines the synthesis of Mn₅(PO₃(OH))₂(PO₄)₂⋅4H₂O particles (MnPhos) by reflux method, it was proposed their addition into waterborne polyurethane and used as hybrid coatings to improve the barrier properties of AISI 1018 carbon steel substrates. The effect of different MnPhos amounts (2, 4 and 6 wt.%) and dispersion times (30, 60 and 120 min) on the corrosion properties in chloride medium (3.0 wt.%) were determined using electrochemical impedance spectroscopy (EIS). Additional characterizations to evaluate changes in the structural, morphological, UV absorption and mechanical properties were realized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet visible spectroscopy (UV–vis), nanoindentation and adhesion test were also evaluated. MnPhos particles correspond with a monoclinic structure and a prismatic morphology of ˜10 μm in length. The addition of MnPhos particles into the waterborne polyurethane (WPU) matrix helps to reduce the polymer degradation under UV-light by inducing a microphase separation phenomenon between the hard and soft segments. Mechanical and corrosion properties also increased by incorporating different amounts of MnPhos particles but, an adequate modulation in the final properties was observed with an amount of 4 wt.% after 30 min of dispersion.