Smart organic/inorganic sol-gel nanocomposite containing functionalized mesoporous silica for corrosion protection

Mesoporous silica nanoparticles were functionalized by Eriochrom Black T (ECBT) as corrosion inhibitor. Next, the functionalized nanoparticles were loaded into the sol-gel coating in order to obtain smart coating system for Ti-Zr pretreated mild steel. Successful synthesis and functionalization of the nanoparticles were confirmed by FESEM, FTIR, and BET methods. EDS-mapping showed that the Ti-Zr pretreatment layer is mainly composed of O, Fe, Ti, and Zr atoms with uniform distribution over the surface. The SEM images revealed that the pure sol-gel coating has micro sized defects but dense silica film without any micro defects or cracks was obtained after incorporation of the functionalized nanoparticles in 0.2 wt. % concentration. The cross-sectional SEM images showed that the coatings are composed of a thin pretreatment layer and a micrometric silica layer. The average roughness of the sol-gel coating was decreased from 179 to 146 nm by incorporation of the functionalized nanoparticles due to the formation of uniform and compact silica structure. The EIS experiments were executed in 3.5 wt. % NaCl aqueous electrolyte to examine the influence of the functionalized nanoparticles on the corrosion behavior of the silane film. It was found that the resistance of the sol-gel coating against corrosion is positively influenced by incorporation of the functionalized nanoparticles so that, the Z(0)(.)(001H)(z) value of the coating containing functionalized nanoparticles was about 2.7 and 6.4 times higher than those obtained for the pure and unmodified silica containing coatings after 24 h immersion, respectively. Improvement of the corrosion resistance was attributed to the releasing of the ECBT molecules from the functionalized nanoparticles and their adsorption on the active corrosion sites. Uv-vis analyses showed that ECBT releasing is a pH-sensitive process implies the smart nature of the sol-gel nanocomposite. The results of the corrosion tests were confirmed by the SEM analyses at the end of the corrosion examinations.