Portugaliae
Electrochimica Acta

Corrosion inhibition action of CGS, namely, PPAB, HPAB, DDPAB and HDPAB, on MS in 1 N HCl, has been investigated. The compounds were synthesized in laboratory, and their influence on MS corrosion inhibition was investigated by WL, PDP and EIS techniques. Ea and ΔGads values of all compounds were calculated, in order to investigate the corrosion inhibition mechanism. The studies revealed that all the compounds inhibited MS corrosion by blocking its active sites. The inhibitors adsorption onto the MS surface in HCl was found to obey the Langmuir’s isotherm. CGS IE(%) was found to vary with their nature and C, and the HCl T, IT and C. Maximum IE(%) was 99.7%, for HDPAB (250 ppm), which had the lowest CR, i.e. 0.15 mmy-1. Keywords: adsorption, CGS, HCl, MS and WL.

This study examined the use of LLE as an inhibitor for MS in a HCl medium, using the optimization approach. In order to determine the metabolites presence, phytochemical analyses were performed on the plant extract. Three variables factors were considered for the optimization: inhibitor C (0.2- 0.8 g/L); T (30-50 ºC); and time (2-6 h). Morphological structure was determined using SEM. Phytochemical analysis results showed the presence of saponins, alkaloids and flavonoids, which confirmed the extract as a good inhibitor. The optimal process conditions were T of 48.30 ºC, time of 2.49 h and C of 0.66 g/L, for obtaining the highest IE of 84.2 %. Meanwhile, the validated OPL gave an IE of 85.6 %. The results observed from SEM showed that a more protective film was formed on the MS surface, in the validated process level. LLE adsorption obeyed Langmuir’s isotherm, and the thermodynamic parameters were: ∆Gads (-17.05, -18.74 and -15.35 kJ/mol-1) and ΔH (41.73, -15.41 and -1.58 kJ/mol-1). ∆Gads negative values indicated LLE spontaneous adsorption, which was physisorption. It can be concluded that LLE would be recommendable as a low-cost inhibitor for MS corrosion in 1 M HCl. Keywords: corrosion; inhibition; LLE; SEM; optimization; phytochemical analyses; RSM.

AS inhibition effect on the corrosion behavior of AA in a 3.5% NaCl solution was herein studied using electrochemical, thermodynamic, surface analysis and DFT (B-3LYP, at 6-31G (d, p)) techniques. The obtained results showed that AS inhibited AA corrosion process. Maximum IE(%) of around 85% was reached with AS C of 1 g/L, and it was stable as T increased from 298 to 328 K. Furthermore, AS acted as a mixed-type inhibitor through electrostatic interaction (physical adsorption), which was more dominant than chemical adsorption, between the charged molecules and the AA surface. EIS measurements confirmed these results. SEM coupled with EDX showed that AS were preferentially adsorbed onto the AA surface. AFM results demonstrated that Ra values were reduced from 338 μm to 79 nm. X-RD offered suitable support to PDP and EIS studies. There was an excellent agreement between experimental and computed data. Pc effectiveness was investigated by DFT studies, having followed the order: GA > D-M. Keywords: 3.5% NaCl, AA, AFM, AS, DFT, EDX, EIS, corrosion, IE(%), PDP, SEM and X-RD.

Two quinoxalinone derivatives, namely 3- (p-tolyl)-3.4-dihydroquinoxalin-2-(1H)-one (Q1) and 3-(4-chlorophenyl)-4-methyl-3.4-dihydroquinoxalin-2-(1H)-one (Q2), were used and investigated as potential corrosion inhibitors for OS in a 1 M HCl solution, at C from 10-6 to 10-3 M, using PDP, EIS measurements and GQCD calculations. EIS results indicate that Q1 and Q2 IE(%) increased with higher C and reached maximum values of 86.2 and 92.5%, at 10-3 M, respectively. The inhibitors adsorption mechanism onto the OS surface was found to obey the Langmuir’s adsorption isotherm model. PDP data displayed that Q1 and Q2 acted as mixed inhibitors, predominantly of the cathodic type. The theoretical results showed that the obtained parameters were in good agreement with the experimental data. Q2 compound had better IE(%), due to the inductive effect of CH3 electro-donor group in dihydroquinoxaline position. Keywords: corrosion inhibition, GQCD calculations, HCl, OS, PDP/EIS and Quinoxalinone derivatives.

Abstract IE(%) of CORP (with AN of 7.8 and 3.5., and modified with Zn powder, MGr or MCNT) used as coatings against CS atmospheric corrosion has been investigated. The studies were carried out by gravimetry and PSP methods. CORP composition was: phosphatides, hydrated oil and SF. IE(%) effect of CO coatings with the investigated compositions on CS corrosion kinetic parameters was estimated in a 0.5 M NaCl solution. Zn powder (50 wt.%) addition to CORP increased their IE(%) up to 80-86%. In this case, the coatings IE(%), at an anodic E of -0.2 V, reached 93-99%. The addition of MGr or MCNT to CORP modified by Zn powder had mostly a negative effect on IE(%). Keywords: anticorrosive composition, low-EA CO, MGr powders and Zn.