Influence of embedded inhibitors on the corrosion resistance of zinc coated with mesoporous silica layers

The aim of this work was to prepare and investigate the corrosion behavior of mesoporous silica layers hosting inhibitor molecules (1H-benzotriazole, BTA and cetyltrimethylammonium bromide, CTAB), which were impregnated into the porous coatings from their aqueous solutions. The mesoporous silica layers were prepared by sol–gel dip-coating method on zinc and (for comparison) on glass substrates using two different pore-forming agents (CTAB and Pluronic PE 10,300). The permeability of one (mono-) and two (bi-) deposited layers was studied by measuring the refractive indices of impregnated samples using optical spectroscopy method. Coatings showed significant permeability to CTAB molecules regardless of the template used. Surface morphology of the samples on zinc substrates was investigated by scanning electron microscopy. The pore structure of the coatings developed with two different surfactants was studied by high resolution transmission electron microscopy. In some cases, the inhibitors were trapped in the impregnated samples by hydrophobizing the layers with dimethyldichlorosilane. Wettability of the silylated coatings was investigated by the sessile drop method. For water and an aqueous solution of Na2SO4 were obtained contact angles above 90°, which confirm the hydrophobic character of the samples. The corrosion behavior of the samples was monitored by electrochemical methods. It was found that the inhibitor containing coatings show higher corrosion inhibiting effect than the native porous silica layers. Moreover, the corrosion current densities decrease by one order of magnitude by rendering the surfaces of the inhibitor containing samples hydrophobic. Interestingly, BTA did not significantly accumulate in the pores, but its presence in the coatings caused increased protection against corrosion.