On the structure of high performance anticorrosive PMMA–siloxane–silica hybrid coatings

Abstract

Environmentally compliant organic–inorganic hybrid coatings for efficient corrosion protection of metallic surfaces are potential alternatives to the current method based on chromate passivation.

Organic-Inorganic Hybrid Coatings for Corrosion Protection of Metallic Surfaces

“…More specifically, regarding the epoxy-silica hybrid system, the results presented in this work and those listed in Table 7 show that different compositions applied to distinct alloys can provide a very effective long-term corrosion protection [7,26,27]. Very promising results were also achieved for PMMA-silica coatings [8,10,31], with the highest observed durability of more than 560 days in 3.5% NaCl, and for hybrids containing reinforcement and inhibitor agents [11,18]. Moreover, for some polyurethane-silica and polyurethane-zirconia-silica systems, it has been demonstrated that they also have a high potential to be used as efficient anticorrosive barrier layers [9,32].…”

“…After optimizing also the ethanol-to-water ratio of the inorganic phase to a value of 0.2, the corrosion resistance and lifetime were further increase to 196 days in 3.5% NaCl (M8_4h_E0.2 coating, Table 4) [10]. Other important finding was the improvement of the corrosion resistance by hot deposition (M8_T80B0.01), which enhances the reaction between the inorganic phase and the metal substrate, improving the coating adhesion.…”

“…Varying the MMA/MPTS molar ratio from 2 to 10, NMR and SAXS results have shown that the M8 sample (MMA/MPTS = 8) presented the highest degree of polycondensation (83.9%) of the silica nanoparticles with an average radius of 0.8 nm, spaced by PMMA segments over an average distance of 4.6 nm. This coating exhibited also an excellent adhesion to the substrate (detachment force > 3.5 MPa) and the best anti-corrosion performance [10,22]. EIS and potentiodynamic polarization results have shown that the M8 coating deposited on carbon steel acts as a very efficient corrosion barrier, increasing the total corrosion resistance by almost 6 orders of magnitude (>1 GΩ cm 2 ) and reducing the current densities by more than 4 orders of magnitude (<0.1 nA cm −2 ), compared to the bare steel substrate [22].…”

“…Structural analysis of PMMAsilica hybrids, performed by AFM, SAXS, NMR and XPS, has shown that the nanostructure is formed by a dense amorphous network of ramified silica-siloxane cross-link nodes, covalently interconnected by short PMMA chain segments [10,22]. Varying the MMA/MPTS molar ratio from 2 to 10, NMR and SAXS results have shown that the M8 sample (MMA/MPTS = 8) presented the highest degree of polycondensation (83.9%) of the silica nanoparticles with an average radius of 0.8 nm, spaced by PMMA segments over an average distance of 4.6 nm.…”

“…For the market, however, which aims on economic and efficient solutions, elevated thickness, and complexity of the coating system, implies elevated material costs and weight increase, issues that are hardly to be accepted, especially by the aerospace industry. In this regard, dos Santos and coauthors [10] have successfully prepared highly efficient PMMAsilica coatings having a thickness of only ~2 μm, which were able to withstand aggressive saline/acid (0.05 mol L −1 NaCl + 0.05 mol L −1 H 2 SO 4 ) and 3.5% NaCl environments for up to 105 and 196 days, respectively, maintaining the corrosion resistance in the GΩ cm 2 range. 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.…”