Corrosion protection performance and interfacial interactions of polythiophene/silanes/MnO2 nanocomposite coatings on magnesium alloy in marine environment

The silane functionalized MnO2 nanoparticles were incorporated in polythiophene (PT) to produce PT/silanes/MnO2 nanocomposites. The surfaces of MnO2 nanoparticles were modified with ethyltrimethoxysilane (ETMS), 3-glycidyloxypropyltrimethoxysilane (GPTMS), and 3-aminopropyltrimethoxysilane (APTMS) and characterized by X-ray diffraction (XRD) studies. The corrosion resistance of newly synthesized PT, PT-ETMS/MnO2, PT-GPTMS/MnO2, and PT-APTMS/MnO2 composite coatings of magnesium alloy (AZ91A) was evaluated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) studies, and scanning electrochemical microscopy (SECM) immersed in natural seawater for several days. The PT-APTMS/MnO2 nanocomposite coatings showed an excellent resistance against corrosion with a charge transfer resistance of over 7517.85 kΩ cm2, which were higher than that of the PT coating (548.25 kΩ cm2) after 80 days immersion in seawater. The coating with MnO2 nanoparticles modified by APTMS, GPTMS, and ETMS groups showed no significant penetration by corrosive ions during 80 days' immersion due to the strong chemical bonding between amino/epoxide/ethyl groups on MnO2 and the sulfur of PT. Decreased current was detected at the scratch of investigated nanocomposite coatings by SECM analysis. The affinity between PT and silanes/MnO2 nanoparticles is enhanced due to their interfacial interactions, which improves the dispersion of silane functionalized MnO2 nanoparticles in PT to produce uniform coatings. Scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) and XRD technique of synthesized nanocomposite coatings confirmed the presence of corrosion products which block the dissolution of Mg alloy. Excellent mechanical properties are shown by the investigated coatings.HighlightsNewly synthesized polythiophene (PT), PT-ETMS/MnO2, PT-GPTMS/MnO2, and PT-APTMS/MnO2 composite coatings on magnesium alloy (AZ91A) was evaluated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) studies, and scanning electrochemical microscopy (SECM) immersed in natural seawater for several days.The addition of MnO2 in the polymer resulted in the reduction of porosity of the coatings significantly.The silane functionalized MnO2 nanoparticles loaded nanocomposite coatings demonstrated excellent resistance against corrosion than that of the MnO2-free PT coating after 80 days of immersion.The corrosion resistance of the coatings was considerably improved due to enhanced interfacial interactions between silane functionalized MnO2 nanoparticles and PT by chemical bonding.The coating with MnO2 nanoparticles modified by amino (APTMS), epoxide (GPTMS), and ethyl (ETMS) groups showed no significant penetration by corrosive ions during 80 days' immersion due to the strong chemical bonding between amino/epoxide/ethyl groups on MnO2 and a sulfur heterocycles of PT without changing the original crosslinking structure of PT.Interfacial interaction between phases also plays a key role in the affinity between MnO2 and PT, which determines the dispersion of MnO2 in coatings and uniform morphology of composite coatings.