CONICET | Buscador de Institutos y Recursos Humanos

Microbiologically influenced corrosion affects industrial systems and in particular the oil industry, implying high costs [1]. During exploitation, the corrosive conditions of the water, the high temperatures and pressures, the salinity, the concentration of suspended solids and the bacteria present in the well provide aggressive enough conditions to generate corrosion. In the storage stage, the proliferation of aerobic microorganisms with surfactant properties is promoted by the availability of various nutrients (water, moisture, oxygen, mineral additives), which can lead to a decrease in the quality of the product, formation of sludge and deterioration of pipes, filters, valves, etc. Protective coatings with a "barrier effect" such as epoxy paints are often used, accompanied by cathodic protection, in pipelines and tanks. This work introduces a new approach through the use of nanostructured zeolite/silver composite (NZSC) as a biocidal additive for epoxy coating formulations. Silver nanoparticles (NPs) dispersed in crystals of zeolite A were prepared by a controlled thermal treatment to an Ag+-exchanged zeolite. Epoxy resin was used as the matrix. The curing agent was a polyamide. An NZSC was added to the epoxy resin using a high-speed dispersion device. To prevent zeolite crystal agglomeration, a dispersant agent based on soya lecithin was employed. Then, the curing agent was added to the resin (1/4 by volume) and dispersed ensuring laminar flow. Five epoxy coatings containing 0, 1, 4, 5 and 8 (%w/w) of silver zeolite were prepared (A, B, C, D and E, respectively). The coatings were applied by spray over metallic substrates (SAE 1010, 1x1 cm, grade A) previously degreased and sanded to Sa 2 1/2° (SIS 05 59 00/67; Rm, 35 μm). The microbiological activity against P. aeruginosa was statistically measured by cell quantification in the biofilm. TEM, XRD and UV-Vis showed the presence of rounded crystalline Ag0 and Ag2O NPs, homogeneously dispersed on the outer surface of the zeolite crystals that coexist with non-crystalline Agmn+ clusters hosted within the porous structure. The SEM images of the cured coatings corroborated a good distribution of the hydrophilic crystals in the dry film, provided by the incorporation of the adequate dispersant. The antimicrobial properties depended on the concentration of the biocide. Coating E promoted effective protection up to six orders of magnitude relative to the control coupon (A). No inhibition halo was observed, then the inhibition mechanism was exerted by direct contact of the coating with the bacterial cells. The aesthetic properties of the coating films were preserved since no dark zones promoted by silver oxidation were observed. Coatings formulated with the silver compound could be effective in controlling the corrosive action caused by P. aeruginosa, minimizing the proliferation and consequently the production of metabolic substances such as corrosive organic acids or biosurfactants.

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