Hybrid sol-gel coatings containing nanoclays for corrosion protection of mild steel

SILVIA CERÉ; IANINA SANTANA; ANDRÉS PEPE; SERGIO PELLICE

Troia

Simposio; 11th International Symposium on Electrochemical Methods in Corrosion Research (EMCR 2015); 2015

International Society of Electrochemistry

Since the adoption of new regulations towards protection of the environment, the use of chromate based coatings is highly limited. So, the development of new environment-friendly high performance anticorrosive coatings is a significant topic for the scientific researchers. In this context, coatings containing lanthanides elements like Ce and La are considered since they potentially can provide a good anticorrosive protection by means of a self-healing mechanism. Sol-gel coatings are compatible with a variety of substrates and can be applied as very thin films having high physicochemical and thermal stability and being possible to be functionalized with a large variety of additives. The barrier properties of sol-gel coatings can be substantially improved by controlling the crosslinking density of its structure or by incorporation of nanoparticles that, in turn, can work as mechanical reinforcement. However, the structural modification introduced by lanthanide compounds on the silica network leaves an open path to the water diffusion through the coating. In the last years, the development of new nanocomposites was highly explored by the use of nano-clays due to its high availability and economical convenience. Those nanoparticles are highly employed as rheological modifiers in the industry of cosmetic and paints and, at the same time, their use as load for composite materials can improve both the mechanical and barrier properties. However, the use of nanoclays in the field of sol-gel coatings is an area that has not been extendedly analysed.In this work nanostructured hybrid films were synthesized by the sol?gel route from tetraethoxysilane (TEOS) and 3-glicidoxipropyl-trimetoxisilano (GPTMS) using laminar nanoclays (Laponite Na0,7[Si8Mg5.5Li0.3H4O24]-0,7) to improve mechanical and barrier properties, and Ce(NO3)36H2O as a supplier of Ce(III) to provide an inhibiting effect in the event of coating failure. Carbon steel plates, AISI 1010, were used as substrates. Prior to the application of the coating, samples were treated with a phosphoric acid 2 % v/v in order to improve coating adherence.In order to evaluate cerium effect, electrochemical behaviour of films containing Laponite and cerium salts (TGLaC) were compared with films containing only Laponite (TGLa) by means of potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) measurements using a 0.35 wt% NaCl solution. Microstructural characterization, surface analysis of substrates and sol-gel coatings were performed by optical microscopy and by XPS techniques.