Inhibitive effect of sodium (E)-4-(4-nitrobenzylidenamino) benzoate on the corrosion of some metals in sodium chloride solution

The inhibition performance of a novel anionic carboxylic Schiff base, sodium (E)-4-(4-nitrobenzylideneamino)benzoate (SNBB), was investigated for various metals, namely low carbon steel F111, pure iron and copper, in neutral 10 mM NaCl solution. Potentiodynamic polarization, scanning vibrating electrode technique (SVET), quantum chemical (QC) calculation, and molecular dynamics (MD) simulation were employed. The potentiodynamic polarization data showed that SNBB acts as an effective corrosion inhibitor for both iron and F111 steel, but it is not effective for the copper. In situ spatially-resolved SVET maps evidenced a major change in surface reactivity for Fe and F111 steel immersed in 10 mM aqueous solution in the absence and in the presence of SNBB. Featureless ionic current density distributions were recorded in the presence of SNBB at both their spontaneous open circuit potential (OCP) and under mild anodic polarization conditions, while major ionic flows were monitored above the metals in the absence of SNBB. On the basis of computer simulations, it is proposed that SNBB produces a stable chelate film on iron and steel surfaces that accounts for the good corrosion inhibition efficiency observed. The different inhibition efficiencies of SNBB molecules on the iron and copper was attributed to the special chemical structure of SNBB molecule and its different chelation ability with the released metal ions on the metal surface. The QC calculations also confirmed the high corrosion inhibition efficiency of SNBB. The MD simulation indicated higher binding energy of SNBB on iron surface compared to that of copper surface. The interaction mode of SNBB on iron and F111 steel surfaces corresponds to a mixed chemical and physical adsorption, and it obeys the Langmuir isother

Active corrosion protection coating for a ZE41 magnesium alloy created by combining PEO and sol-gel techniques

An active protective coating for ZE41 magnesium alloy was produced by sealing an anodic layer, loaded with 1,2,4-triazole, with a sol-gel film. An anodic oxide layer was formed using PEO in a silicate-fluoride alkaline solution. This thin (1.8 mu m) porous PEO layer was impregnated with corrosion inhibitor 1,2,4-triazole and sealed with a silica-based sol-gel film modified with titanium oxide. For the first time it was demonstrated that this relatively thin PEO-based composite coating revealed high barrier properties and provided superior protection against corrosion attack during 1 month of continuous exposure to 3% NaCl. A scanning vibrating electrode technique showed a sharp decrease (100 times) of corrosion activity in micro defects formed in the 1,2,4-triazole doped composite coating, when compared to blank samples

Corrosion protection of AA2024 by sol-gel coatings modified with MBT-loaded polyurea microcapsules

In this work we report the synthesis of polyurea microcapsules loaded with corrosion inhibitor 2-mercaptobenzothiazole (MBT) for corrosion protection of 2024 aluminum alloy. The microcapsules were prepared by interfacial polycondensation. The resulting capsules exhibit spherical shape, with diameter ranging between 100 nm and 2 mu m. The loading content of MBT was found to be 5 wt% and release studies showed that MBT is preferentially released under acidic and alkaline conditions and follows a Fickian diffusion model. This pH dependency seems suitable for protection of metallic alloys where corrosion processes are accompanied by local pH changes. Furthermore, the microcapsules were added to a hybrid sol-gel coating and its performance assessed by electrochemical and accelerated standard tests. The results obtained indicate that capsules loaded with MBT do not affect negatively the barrier properties of sol-gel coatings, and contribute for the enhancement of adhesion of coatings to the metallic substrate. More relevant, these additives impart active corrosion protection suppressing corrosion activity at defect sites, which opens prospects for application of polyurea microcapsules as additives for high-performance coatings. (C) 2015 Elsevier B.V. All rights reserved