Estudo da influência dos organossilanos TEOS e APS, associados ao inibidor orgânico AMT, na resistência à corrosão de aço carbono AISI 1020 em meio salino

Abstract

This thesis proposes a study for the production of coatings with different combinations of tetraethylorthosilicate (TEOS) and 3-aminopropyl-trimethoxysilane (APS) silanes, associated with the corrosion inhibitor 5-amino-1,3,4-thiadiazole-2-thiol (AMT), on AISI 1020 carbon steel, in order to increase the corrosion resistance of this material in a saline medium. Initially, the steel samples were pre-treated in AMT 10-2 mol L-1 solution for 3 hours. Subsequently, the same samples were immersed in 5% v/v APS solution and/or 5% v/v TEOS in dip coating, using a 14 min immersion time for each step. The immersion of the substrate in APS and/or TEOS was carried out twice to produce coatings with two layers of silane. Between each immersion in the silane solution, AMT/APS (two layers; Group I), AMT/TEOS (two layers - Group II), AMT/TEOS/APS (one TEOS layer/one APS layer - Group III), and AMT/APS/TEOS (an APS layer / a TEOS layer - Group IV) were heat-treated in an oven, at different temperatures (50, 100 and 150ºC) and curing times (40, 80 and 120 min), in order to verify the effect of these parameters on the anticorrosive performance of the prepared systems. The coatings produced were initially characterized electrochemically using electrochemical impedance spectroscopy (EIE) in 0.5 mol L-1 NaCl. Those that showed the best results concerning the corrosion resistance were also evaluated by potentiodynamic polarization (PP) in the same electrolyte. Analyzes of scanning electron microscopy (SEM), X-ray dispersive energy spectroscopy (EDS), and contact angle measurements were performed to evaluate the morphology, composition, and hydrophobicity of the coatings. The films produced under the conditions of Experiments (Steel/AMT/APS - 100ºC; 80 min), (Steel/AMT/TEOS - 100ºC; 80 min) and (Steel/AMT/APS/TEOS - 100ºC; 120 min) showed the best anti-corrosion properties among all those studied in their respective groups. Regardless of the curing conditions used, the results indicated that, under these conditions, the presence of the inhibitor favored the formation of more protective coatings. XPS analyzes performed on systems 2 (Steel/AMT) and 8 (Steel/AMT/APS) showed the formation of the chemical bond Fe-O-S-R, confirming the interaction of the AMT inhibitor with the surface of the steel treated with NaOH. The results obtained allow us to propose that the APS-AMT interaction may have occurred from the N-S link identified in the N1s spectrum. Among all the systems presented in Groups I, II, III and IV, sample 8 (Steel/AMT/APS - 100ºC and 80 min) showed the best anti-corrosion properties proven by electrochemical tests (Rct = 2867 Ω cm2; Cdl; 8,50x10-5 F cm-2; jcorr = 5.36x10-6 and Ecorr = -0.598V) and was used as a primer for a painted system. The pull-off test and salt spray tests showed that even with a slight reduction in the rupture stress values when compared to the Steel/epoxy coating (23.93 MPa), the painting schemes containing the APS silane (22.58 MPa) and the AMT/APS set (23.19 MPa) maintained the same nature of failure (Type B Cohesive), reflecting in the lower corrosion advance values after 1000h of exposure in the aggressive atmosphere.