Structural properties of cerium doped siloxane–PMMA hybrid coatings with high anticorrosive performance

Abstract

Novel environmentally compliant Ce(IV) doped siloxane-PMMA coatings exhibiting dense cross-linked structure, high thermal stability, unique anticorrosive performance and self-healing ability.This study reports on the characterization of cerium doped organic-inorganic hybrid coatings by correlating their structural properties with the corrosion protection efficiency of coated carbon steel.The films were prepared via the sol-gel route from radical polymerization of methyl methacrylate (MMA) with 3-methacryloxy propyltrimethoxysilane (MPTS) followed by acidic hydrolysis and condensation of tetraethoxysilane (TEOS). After identifying the optimum proportion of polymeric and silica phase for the formation of a highly ramified structure (MMA/TEOS = 4), increasing concentration of Ce(IV) ions (0.1% < Ce/Si < 5%) was added to the inorganic precursor to enhance the passivating character of the films. Nuclear magnetic resonance, X-ray photoelectron spectroscopy, small angle X-ray scattering, atomic force microcopy and thermogravimetry were used to characterize the structural properties and electrochemical impedance spectroscopy, potentiodynamic polarization curves and field emission scanning electron microscopy were employed to evaluate the corrosion resistance of the coated samples in standard saline environment. Structural analysis revealed a high degree of connectivity of the hybrid network, resulting in an enhanced thermal and electrochemical stability of the material. Detailed investigation of the structural effect of cerium species revealed that reduction of Ce(IV) ions during the polycondensation process catalyzes an increase of siloxane network connectivity (>87%) and enhances the polymerization of organic moieties. The electrochemical assays showed that the coatings posses an excellent long-term stability at high corrosion resistance of up to 10 GΩ cm 2 and current densities about 6 orders of magnitude lower than that of the bare carbon steel. For elevated Ce(IV) doping levels the self-healing ability was observed preventing during long-term exposure further progression of the corrosion process.

Organic-Inorganic Hybrid Coatings for Corrosion Protection of Metallic Surfaces

“…The excellent performance of the primer free coating was explained by the high connectivity of reticulated sub-nanometric silica domains densely interconnected by short PMMA chain segments. Another results that confirmed the viability of thin hybrid films as efficient corrosion barrier have been reported in the study of Harb et al [11]. The authors showed that the addition of cerium (IV) salt into PMMA-silica system results in a further improvement of the corrosion resistance and durability of the coatings applied to polished carbon steel by dip-coating.…”

“…Detailed investigation of the structural effects of cerium species has shown that reduction of Ce(IV) ions not only catalyzes a higher connectivity of the silica phase, but also enhances the polymerization of organic moieties. The resulting enhancement of the overall network connectivity leads to an improvement of the thermal stability of the hybrids, as evidenced by the results of the thermogravimetric analysis [11].…”

“…After identifying the optimum proportion of polymeric and silica phase for the formation of a highly ramified structure (MMA/MPTS/TEOS molar ratio = 8/1/2), increasing molar percentage of Ce(IV) ions (0.1% < Ce/Si < 5%) have been added to the inorganic precursor to enhance the passivating character of the films [11]. Table 5, have revealed the active role of Ce(IV) in the PMMA-silica matrix.…”

“…A number of studies report on the use of cerium salts (chloride and nitrates) and ceria nanoparticles as inhibitors, preventing corrosion by the selfhealing ability in affected areas of inorganic, organic, and hybrid coatings. The resulting substantial lifetime increase is attributed to the formation of insoluble oxides and hydroxides in the corroded zones [3,11,[14][15][16][17]. On the other hand, significant improvements of thermal and mechanical properties have been achieved by incorporation of clays, lignin, carbon nanotubes, graphene oxide, and graphene into polymeric or organic-inorganic matrices [18][19][20].…”

Native Oxide Films on AZ31 and AZ61 Commercial Magnesium Alloys – Corrosion Behaviour, Effect on Isothermal Oxidation and Sol–gel Thin Film Formation

“…Recently, Harb et al have reported a similar study where they also correlated the structural properties of cerium doped organic-inorganic hybrid coatings with their efficiency for the corrosion protection of carbon steel. The films were prepared via the sol-gel route from radical polymerisation of methyl methacrylate with 3-methacryloxy propyltrimethoxysilane followed by acidic hydrolysis and condensation of tetraethoxysilane [37]. A promising research line consists in introducing phosphorus precursors into organic-inorganic hybrid sol-gel coatings.…”