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.

This work examined MLE as Zn corrosion inhibitor in a NaOH medium. MLE was subjected to qualitative and quantitative Pc analyses. Thermometric and gravimetric techniques were employed in the corrosion inhibition study. In the thermometric method, reaction numbers for Zn dissolution in blank and inhibited NaOH media were used to determine MLE IE(%). The gravimetric method was carried out using one factor at a time and RSM. CCD of DES was employed in RSM. The analyses of the experimental results revealed that MLE was predominantly made up of flavonoids, alkaloids and tannins (471.7, 458.3 and 115.0 mg/100 g, respectively). Zn  by the extract increased with higher inhibitor C, but decreased with a rise in T. A quadratic model adequately described the relationship between IE(%), C, T and time factors. High IE(%) of 83.75% was obtained at an inhibitor C of 1.0 g/L, T of 303 K and IT of 5 h. Hence, MLE is a suitable inhibitor for Zn corrosion in a NaOH medium. Keywords: corrosion inhibitor, MLE, NaOH and Zn.

The present study has investigated electrolysis conditions, in which spatiotemporal structures onto the cathode surface could be observed for the first time, under strictly controlled settings, during Cu-Sb alloy ED. Self-organization phenomena, such as in depth self-assembled deposits structures, appeared when Sb content was higher than 70 wt% in the coatings. The layers and their structures different optical and morphologic areas were characterized. Keywords: Cu-Sb alloy; ED; multilayers; self-organization.

Inhibition of MS corrosion in a 3% NaCl solution, by glasses containing Ti-0, Ti-5 and Ti-7, in different C, was investigated using AFM, EIS, FTIR spectroscopy, PPD, SEM and XRD techniques. PPD and IES gave IE(%) of 92.8, 99 and 98.3%, and 91.9, 98 and 98.3%, for Ti-0, Ti-5 and Ti-7 glasses, respectively, at optimum C (0.4 g/L). In addition, EIS results indicated that IE(%)increased with higher C of Ti in the glasses, reaching its maximum at 7% TiO2. The three studied compounds acted as anodic inhibitors, though anodic reactions were more suppressed than the cathodic ones. SEM revealed that the inhibitors significantly stopped the attack by Cl- ions, through chemical adsorption onto the MS surface. Keywords: Ti-0, Ti-5 and Ti-7 glasses; MS; 3% NaCl; AFM; EIS; FTIR; PPD; SEM; XRD.

U2 and U4 were successfully synthesized from C7H6N2 N-alkylation (general and useful route to quaternary ammonium salts NH4Cl from tertiary amines) with alkyl bromides. The products were further alkylated to the corresponding ILs: U5 and U7. All the synthesized compounds were characterized by spectroscopic techniques, and their compositions were established through elemental analysis. The synthesized compounds were investigated as inhibitors for MS corrosion, using 1 M HCl as a model solution. WL experiments, surface analysis, quantum chemical calculations and MD simulation methods were used for evaluating the inhibitors anticorrosion properties. The results showed that ILs possessed remarkable inhibition properties under the studied conditions. U5 displayed the highest IE of 95.22%, at 200 ppm. ILs corrosion IE(%) was ascribed to their adsorption onto the MS surfaces, which followed the Langmuir’s isotherm. SEM revealed the formation of a barrier film by the inhibitors on the MS surface. Finally, the experimental results were corroborated by theoretical quantum chemical calculations and MD simulation studies. The studied inhibitor molecules interaction energies with the Fe surface followed the order U5 > U7 > U2 > U4, which is consistent with the experimental data. Keywords: corrosion inhibition, ILs, MD simulations, MS, N-alkylbenzimidazoles, quantum chemical calculations and SEM.

MS acceptability for nowadays structural construction is premised on its availability and low cost. However, due to MS poor corrosion resistance, most especially in acidic and alkaline environments, there have been increasing concerns about its use. The use of inhibitors, as proposed by different researchers, mitigates MS CR, thus reducing the economic losses experienced by all chief users of this alloy. In recent years, scientists have focused on green inhibitors obtained from plant, fruit and vegetable extracts, and essential oils. Besides being environmentally friendly, in terms of corrosion resistance, plant extracts are becoming increasingly important, due to their low cost and toxicity, and high availability. Additionally, they are rich in organic compounds with polar atoms, such as O, P, S and N, containing multiple bonds in their molecules, through which they can adsorb onto the metal surface, forming a protective film, by various adsorption isotherms. This paper provides a review on research works done so far on MS corrosion control by naturally occurring plant extracts as corrosion inhibitors, in both acidic and alkaline environments, where this alloy is mainly applied. Keywords: plant extracts; CR; inhibition; MS; adsorption isotherms; environments.

In this study, an alkaloid was extracted from LN leaves. The AE was firstly evaluated as AO, by using a DPPH solution, and comparing it with a BHT standard solution. The AE, at 200 mg/mL, showed high efficiency as AO (93%). Furthermore, it was studied as a CI for an Fe alloy in HCl, at 25 ºC, with different C (1 to 5 ppm). The AE depicted the highest IE(%) of 92.42%, at 5 ppm. T effect on IE(%), for optimal C (5 ppm), was studied at 35, 45 and 55 ºC. The results revealed that the IE(%) decreased with higher T. Additionally, kinetic parameters, such as Ea*, H* and S*, were calculated. Keywords: AE, LN, AO, corrosion inhibitors and DPPH.

MS effective corrosion inhibition by SVLE has been investigated using electrochemical methods. Tafel polarization measurements suggested that the reaction at the anode occurred with MS dissolution, due to the strong medium aggressiveness, but SVLE addition led to a corrosion IE(%) of 93.6%, at 298 K. SVLE IE(%) still was 86% at an elevated T of 328 K, which was also confirmed by SEM observations that revealed a protective adsorbed film formed by the inhibitor onto the MS surface. Keywords: SVLE, MS, corrosion, polarization curve and high T IE(%).

WO contain many elements that are toxic to the health and environment. WO discharge into the natural environment without any prior treatment can clog the filters in the water treatment stations, disrupting the biological purification processes. It is also forbidden to burn these fluids without pretreating them: their wild incineration releases dioxins and greenhouse gases. In WO recycling process, the final step is to pass it through a press filter containing BT oil treated at a ratio of 10:90. The pressed cake is then abandoned in nature, or transported to the landfill. This study focused on the reuse of BT mud cakes soiled with impurities from recycled WO. A PC study of the pulp properties, followed by a toxicological study, enabled to recommend the reuse of this slurry mud as a tight and very suitable soil covering. Thus, controlled landfills, sports fields and storage tanks for irrigation water can be coated with this compact clay, and prevent seepage into the water table. Our work is divided into two main parts: the first concerned the study of the specific characteristics of BT extracted from WO (permeability, specific surface, porosity, adhesion to the ground and durability); and the second carried out the bacteriological and eco-toxicological study of BT-WO residues, in order to prevent all negative impacts likely to reduce the quality of the soil, groundwater, human health and vegetation. Keywords: WO, surface area, permeability, porosity, waterproofing, eco-toxicity, BT and floor covering.

Issues regarding corrosion have become a substantial source of expenditure for oil and gas industries. Apart from that, oil spillages resulting from leakages in pipelines pose severe environmental challenges, such as pollution and fire outbreaks. A36 LCS is commonly used for fabricating oil and gas pipelines, due to its availability and cost. The aim of this study was to deposit Zn-MgO-xCn CC on A36 LCS substrates, to improve their CRS in acidic media, through the ED route. W corrosion determination technique was used for determining the developed coatings CR. The CC surface morphology and phase evolution were determined by OPM, SME and X-RD. The results showed that all the developed CC offered lower CR values than that of the A36 LCS substrate, which was 5.4392 mm/y. Sample D4 (20 g Zn and 20 g MgO-Cn) had the lowest CR value of 0.7199 mm/y, corresponding to a coating E of 86% on the substrate. Finally, among the developed coatings, sample E1 (Zn and 20 g MgO) gave the highest CR values of 2.1030 mm/y, with an E value of 61%. The study showed that the CC were able to form protective barriers on the substrate in the corrosive media. Keywords: CC, NP, substrates and corrosion.

The increasing challenge of components used for the development of new materials, in order to improve their mechanical performance, can never be over-emphasized. The present research of a produced P-Al2O3 coating grafted into a Zn electrolyte was done through the thin-film alloy ED on MS, in a time range from 15 to 30 min, pH 5 and T of 95±5 ºC. P-Al2O3 morphological properties were characterized by TESCAN SEM and elemental quantification with EDS. The deposited alloy strengthening and dislocation performance were studied using diamond-based Vickers  test and a reciprocated wear slider, under a 5 N load. The pitting corrosion study was made using a PGStat101 auto lab potentiostat galvanostat, by LSV and OCP methods. The results show that P-Al2O3 is an active corrosion inhibitor and adsorption composite. The ED mass was obtained at a significant value of 0.1302 and 0.1567 g, at 25 and 30 min DT. At 30 min, wear loss and CR, along with the interfacial surfaces of this CC, were lower than those of other developed alloys, at 15 min, due to the progressive particulates loading effect. The average significant HVN trend was influenced by the particulates weight fraction precipitation. MS properties enhancement by P-Al2O3 indicated that the CC can be used for advanced industrial applications, especially in corrosive environments. Keywords: adsorption, components, corrosion, MS, P-Al2O3 and protection.

The widespread use of HMDE for multi-ionic analysis is mainly explained by the following factors: excellent reproducibility, due to the electrode surface ease of renewal, for preventing hysteresis; wide Ec; ability to forming amalgams with many redox-active metal ions; and (sub)nanomolar detection limits, which have unique capabilities for multi-metal determination. In this research, selectivity and sensitivity for Pb, Cd and Zn simultaneous determination, by DPAdSV, using HMDE as WE and CCA as a ligand, were tested. This method is based on the deposition of CCA-metals on Hg electrodes. The instrumental and chemical parameters that could improve measurements were obtained under optimal conditions, including: CCA concentration (0.05 mmol/L), pH (7), Edep (-0.3 V) tdep (60 s), AB concentration (0.5 mol/L), scan rate (150 mV/s), pulse height (80 mV), Hg drop size (4 mm2) and linearity (Ip vs concentration), which was in the range from 5 to 170, 5 to 140 and 5 to 190 M, for Pb, Cd and Zn, respectively). The LOD (S/N = 3) values were 0.05, 0.03 and 0.05 µg/L for Pb, Cd and Zn, respectively. The repeatability and intermediate precisions were tested as RSD of 0.44, 1.21 and 1.23% for Pb, Cd and Zn, respectively. The recovery values were 98, 99 and 101% for Pb, Cd and Zn, respectively. As result, the DPAdSV method with CCA ligands was successfully applied for heavy metals determination in the seawater of a former bauxite mining area. Keywords: bauxite, DPAdSV, HMDE, CCA, heavy metals and voltammetry.

SLE (Melastoma candidum D. Don) was tested as an inhibitor of St-37 S corrosion in a HCl solution, using WL, PDP and SEM analysis methods. CR has decreased with SLE addition, according to the WL method. The highest IE(%) was 67%, with 0.8% SLE addition. Rise in T had a decreasing effect on IE(%). PDP showed that the extract was a mixed inhibitor. SEM analysis showed changes in the St-37 S surface immersed in HCl, without and with the inhibitor. SLE adsorption onto the steel surface obeyed Langmuir’s isotherm. Keywords: corrosion IE(%), Langmuir’s isotherm, PDP, SEM, SLE, St-37 S and WL.

Medical forensics and homeland security have been focusing on the food and beverage industries, for water quality remote sensing, drug residue determination in food, etc. NT is playing a growing role in BS development. NT-based BS, also known as NBS technology, are reshaping the medical field. They are used in metabolite measurement, diabetes monitoring, and other applications, such as environmental protection. Pesticide and heavy metal ions detection in river water, as well as genomes sequencing the use of NM in BS design have increased their sensitivity and ability to also develop NP special properties, such as high electrical conductivity, improved shock resistance, sensitive response and flexibility. These advances result from the confluence of NP characteristics, allowing for the presentation of numerous modern flag transduction innovations in BS, such as the development of devices, and forms for manufacturing them and enhancing their measurement capability. Imaging the nanoscale objects has improved sensors connected with tiny atoms. Many mechanical devices, optical resonators and bi-functional architecture based on NBS have been developed. BS have also been discussed in this research, in order to highlight their critical applications in a variety of fields. This study discusses the various types of BS that depend on multiple types of NM, as well as their biological and implicational factors and analytical techniques, such as amperometric, CV potentiometric optical techniques, and other measurements methods that use enzyme and non-enzymatic BS. Keywords: NT application, NBS, BS analytical techniques, enzyme BS and nanoenzymatic sensors.

Two novel synthesized compounds (FD and ACP) have been applied as inhibitors for MS corrosion in HCl and H2SO4 solutions. Gravimetric, PDP, EIS, SEM and theoretical approaches were employed for the investigation of FD and ACP synthesized compounds IE%. Their corrosion IE% and calculated quantum chemical properties were comparable to each other, and indicated that ACP is a slightly less effective inhibitor than FD in HCl and H2SO4 solutions. Langmuir’s, Temkin’s, Frumkin’s and Freundlich’s adsorption isotherms were used for describing the inhibitors adsorption behavior. The adsorption was spontaneous and followed a mixed mechanism, but with initial physisorption. Polarization data revealed that the inhibitors were more cathodic, because they tended to enforce MS HER retardation. The inhibitors decreased the electrolyte impedance, while Rct increased. The adsorption mechanism was influenced by the protonation and solvation environment, and it was concentrated within the heteroatoms and the aromatic systems. Calculated quantum parameters agreed effectively with the obtained experimental results, while FF indices were useful for predicting the nucleophilic and electrophilic attacks positions. Keywords: ACP, adsorption isotherm, corrosion, EIS, FD, IE (%), MS and PDP.