The anticorrosive properties of sol-gel films doped with hydrotalcite nanoparticles applied on tinplate

The use of two-layer system based on the sol-gel technology is proposed as the inner lacquer for tinplate food cans. The primer was a hybrid film based on tetra-n-propoxyzirconium (TPOZ) and 3-Glycydoxypropyltrimethoxysilane (GPTMS) precursors. The topcoat was also a hybrid film based on tetraethyl orthosilicate (TEOS) and vinyltrimethilsiloxane (VTMS) precursors. The topcoat is intended to be in contact with foodstuff, thus, hydrotalcite nanoparticles were incorporated as dopants to increase the film barrier properties. The types of hydrotalcite nanoparticles studied were as-synthesized (HT) and thermally activated (CHT). The zeta potential measurements performed on the hydrotalcite suspensions indicated that they were stable in the acidic conditions used to synthesize the sol-gel solution; therefore, the particles disperse well into the sol-gel.The electrochemical behaviour was evaluated by means of Electrochemical Impedance Spectroscopy (EIS). The results showed better performance of tinplate samples coated with doped sol-gel film than undoped films. However, there were not significant differences between the hydrotalcite types, indicating that the mechanism of inhibition has to be the same in both cases. The zeta potential evolution of HT and CHT suspensions with the NaCl concentration revealed the adsorption of Cl— anion on the particles surface, removing the chloride ions from the surrounding environment.