Synthesis of stabilized dispersion covalently-jointed SiO2@polyaniline with core-shell structure and anticorrosion performance of its hydrophobic coating for Mg-Li alloy

Abstract

A new method was developed in this paper to obtain self-film-forming polyaniline (PANI) grafting SiO2 (SiO2@PANI) sol which could form hydrophobic coatings on the surface of magnesium-lithium (Mg-Li) alloy directly for the purpose of anticorrosion. Firstly, covalently-jointed SiO2@PANI sol with core-shell structure was synthesized with (3-glycidoxypropyl)-trimethoxylsilane (GPTMS) modified SiO2 as core and PANI as shell, and then SiO2@PANI/VTMS sol was prepared after embedded SiO2@PANI with vinyl trimethoxysilane (VTMS). The structure and morphology of SiO2@PANI particle were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The hydrophobic and anticorrosion properties of SiO2@PANI/VTMS coating on Mg-Li alloy were evaluated by contact angle, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The results showed that aniline is polymerizing on the surface of SiO2 preferentially through the reaction between the epoxide group in GPTMS and amino group in aniline. The obtained SiO2@PANI sol dispersed stably in ethanol and supplied well microroughness to coatings, and subsequently enhanced hydrophobic properties of SiO2@PANI/VTMS coatings along with low surface energy supplied by VTMS. The hydrophobic angle of SiO2@PANI/VTMS coatings is high up to 133.8°. Consequently, the coatings have better corrosion resistance performance for the active Mg-Li alloy. Its impedance value is 5 × 104 Ω·cm2, and corrosion current density is merely 6.7 × 10−7 A·cm−2.