Portugaliae
Electrochimica Acta

The inhibitive effect of a seaweed (SM) alcoholic extract on MS corrosion immersed in 1 M HCl, for 30 min, was evaluated by the WL method and PPD technique. The protective film was investigated by the Vickers hardness test. WL revealed that 500 ppm SM offered 84 % IE against MS corrosion in 1 M HCl. The inhibitor molecules adsorption onto the metal surface obeyed Langmuir’s adsorption isotherm. The R2 value was very high (0.998). The PPD study showed that Ecorr slightly shifted to the anodic side. It was inferred that SM functions as a mixed type of corrosion inhibitor, since the shifts were relatively small. In SM presence, LPR value increased and Icorr decreased. Due to the blanket effect (formation of a protective film on the metallic surface, which was found to be a monolayer, blocking anodic and cathodic sites), the electrons transfer from the metal into the solution was blocked. Vickers hardness of the inhibited MS surface was lower than that of the polished one, but higher than that of the corroded one. The outcome of the study may be used in the pickling industry, where HCl is used to remove the rust from the metal surface, simultaneously not attacking it. Keywords: corrosion inhibition, green inhibition, acidic medium, SM, Vickers hardness, isotherms and electrochemical studies.

In this study, Zs-c leaves were extracted by a 70% CH3OH solvent. The extract was investigated as green corrosion inhibitor for CS C1010 alloy in 0.1 M HCl. The study was done with different inhibitor concentrations (1, 2, 8 and 9 ppm). The extract showed the highest IE of 96.06%, at 9 ppm. The inhibitor adsorption on the CS alloy surface was found to obey the Langmuir’s adsorption isotherm model. Kads, ΔHads, ΔSads and ΔGads were also calculated. The temperature effect on Zs-c leaves extract IE%, with the optimal concentration of 9 ppm, was studied at 35,45 and 55 ºC. The results showed that IE% decreased with raising solution temperatures. In addition, E_a^*, ΔH, ΔS and ΔG kinetic parameters were calculated. On the other hand, phytochemical tests and quantitative analysis, such as TPC and TFC, were also carried out. In addition, the anti-bacterial activity or growth inhibition of bacterial strains, such as Ec and Sa, were studied. Anti-fungal activity or growth inhibition studies of Ca and An species were also carried out, at a 100 mg/mL concentration. Anti-oxidant activity was also investigated by DPPH, at concentrations of 100, 250, 500, 750 and 1000 µg/mL, and good results were obtained. Keywords: Zs-c leaves, corrosion inhibitors, phytochemicals, DPPH, Ec, Sa, Ca and An.

DBS corrosion resistance effect on MS immersed in a 0.25 mol/L sulphuric acid (H2SO4) solution has been evaluated at room temperature, using WL method, from which CR and IE(%) were obtained. The corrosion IE% increased with higher inhibitor concentrations. The CR decreased with higher DBS concentrations, since it blocked the MS active site, forming a protective film on its surface, which was confirmed by electrochemical studies and surface analysis techniques, such as FTIR and SEM. EDAX was used to analyze the elements present on the MS surface, after its immersion in 0.25 mol/L H2SO4, without and with DBD. The MS surface smoothness and roughness (polished and corroded) and the inhibitor have been evaluated by SEM and AFM. Keywords: AFM, corrosion, DBS inhibitor, H2SO4, MS, SEM and WL.

In continuation of our previously published work entitled Mechanical and Corrosion Behavior of Inconel 718 Nickel-Based Super Alloy Doped with Graphene Nanoplatelets, the present study investigated the tribological performance of modified IN 718 doped with GrNs. Friction and wear properties were analised using an advance universal tribometer, while surface mophologies were studied by SEM. The modified SA tribological properties validation was done in relative comparison to those of pure IN 718. Mechanical properties with higher , younger modulus values, better morphologies, higher AWI, lower SWR and µ values were noted on the modified IN 718. Nonetheless, an increase in the load proved to affect the tribological oxide layer properties of both pure and modified IN 718. Keywords: pure and modified IN 718, GrNs, frictional wear, tribology and SEM.

DESs, as new-generation room temperature ILs, are very promising to perform anodic processing of different metals and alloys. We report Ni-Cu alloy (45 wt.% Ni) anodic treatment in a DES, ethaline, for the first time. It is shown that the anodic dissolution originated the formation of sparingly soluble Ni and Cu chloride salts in the near-electrode layer. Ni-Cu alloy anodic treatment in ethaline resulted in changed patterns of the metallic surface morphology. Depending on the applied electrode E, star like crystallites, with sharply pointed shapes and thorns, may appear on the anodically etched surface, and surface morphology smoothing was observed, in some cases. The Ni-Cu alloy anodic processing in ethaline, which dramatically changed its surface morphology, contributed to a considerable increase in the electrocatalytic activity towards HER in an alkaline medium. Considering favorable environmental aspects of DES use and marked improvement in electrocatalytic properties, this treatment can be further used to develop high-efficient, eco-friendly and relatively inexpensive electrocatalysts methods for water electrolysis within H2 energy concept. Keywords: Ni-Cu alloy, anodic processing, ethaline, hydrogen production electrocatalysis.

Welding has been an incredibly important process used to join metals in several industrial applications, such as manufacturing, construction, automotive and aerospace sectors. It has been reported that welded joints sometimes exhibit poor corrosion resistance, due to the changes in the weld surface or HAZ chemical composition, residual stress and metallurgical structure. Therefore, there is a need to enhance welds corrosion resistance and microstructure properties through PWHT. In this study, PWHTs effect on the corrosion and microstructure properties of two MSs, SAE 1015 and 1010, which were fused by electric metal arc welding, was examined. The MS samples, with different chemical compositions, were cut to the desired dimensions, separately welded and, thereafter, subjected to PWHT, at 650, 750, 850 and 950 ºC, for 1 h. The corrosion and microstructure properties of the PWHT MS samples immersed in 3.5 wt.% NaCl were then investigated, using PDP and SEM, respectively. For the PWHT SAE 1015 and 1010 MS samples, the lowest CR values were 34.240 and 35.793 mm/year, at 650 ºC, while the highest were 90.16 and 60.10 mm/year, at 950 ºC, respectively. For the AW SAE 1015 and 1010 MS samples, the CR values were 107.54 and 118.09 mm/year, respectively. The SEM images revealed smaller grain sizes and boundaries and less porosity for PWHT MS samples at 650 ºC than for those at 950 ºC. Therefore, the first ones are recommended for advanced industrial applications. Keywords: AW MS, corrosion, microstructure, MS SAE 1015 and 1010, PWHT and welding.

Due to its highest gravimetric energy density, H2 has been regarded as the preferred clean-energy carrier, with potentially environmentally-friendly production through the solar-assisted WS. Since human activities generate enormous amounts of WW, H2 production from this new resource has gained attention as an emergent technology. This paper addresses the most relevant and current aspects of H2 production from WWEL, and electricity generation from RES. In this sense, the state of art of H2 production, especially from WS, is presented here, as well as the main approaches to electricity generation from RES, with the greatest potential for viability. A new approach on this matter, which is part of the work that is being developed by the authors of this study, was also herein presented. Keywords: WW, water, electrolysis, H2 and RES.

Abstract Olive mill wastewater (OMW) is the major problem from olive oil extraction, due to its polluting organic and mineral matter and acid pH. This study aims to electrochemically treat OMW in an Al electrode reactor, to oxidize the organic matter, discolor the margins and neutralize the pH, thus reducing the pollutants. Various low cost adsorbents have been studied for the treatment of different types of effluents. In this study, the potential of activated carbon (C) derived from olive stones (OS) was studied for OMW removal. H3PO4 (phosphoric acid) treated OS (AOS), as a low-cost, natural and eco-friendly biosorbent, was investigated for OMW removal from aqueous solutions. This work found that the increase in electrolysis time and current intensity significantly improved the treatment, while energy consumption and electrodes were observed. The results showed thirty-fold diluted margins for effluents with an acid pH of 5.02 and a conductivity of 14.89. The physicochemical parameters evolution during the electrocoagulation (EC) treatment showed that, under the conditions of an electrolysis time of 3 h and a current intensity of 3 A (= 416 A/m-2), the margins discoloration diluted ten times (91%), the mass loss of the electrodes was 0.55 kg.m-3 and the chemical oxygen demand (COD) reduction was 50%. These optimal operational levels allowed a good degradation of the margins. Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The experimental isotherm data were analyzed using Langmuir’s and Freundlich’s isotherms equations. The best fit was obtained by the Langmuir’s model, with maximum OWM monolayer biosorption capacity of 189.83 mg/g. The biosorption was exothermic in nature (entalphy change: H° = -13.11 kJ/mol). The reaction was accompanied by a decrease in entropy (S° = -72.91 kJ/mol). The Gibbs energy (G°) was higher when the temperature was increased from 303 to 318 K, indicating a decrease in the biosorption feasibility at higher temperatures. The results have established good potentiality for EC and ALS to be used for OMW removal. Keywords: OWM, phenol, OS, H3PO4, adsorption, EC, eco-friendly biosorbent, kinetics, equilibrium and thermodynamics.

Abstract The Western Central Valley (WCV) of Costa Rica is an area of interest, due to its high concentration of population and economic activity, presenting itself as a tropical monsoon-type atmospheric basin (AB), with well-defined climatic seasons (dry and rainy). The present study proposes the assessment of low carbon steel (CS) atmospheric corrosion, based on ISO 9223 (2012) and associated standards. A general analysis of the atmospheric basin effect was initially performed on these data, followed by the basic modeling of air pollutants and meteorological parameters. The WCV is an area of low contamination, which corresponds to a C2 or C3 category, according to ISO 9223. It mainly shows significant climatic seasons (dry and rainy) effects on the initial corrosion rates, but obtaining similar annual corrosion results for them. The ISO 9223 annual atmospheric corrosion model overestimated the actual obtained corrosion values, whereas linear or logarithmic models gave better results, especially when time and/or time of wetness (TOW) were considered as variables. Keywords: low CS, mathematical modeling, monsoonal climate, air pollutants, rain, TOW, ISO 9223 and ISO 9225.

Abstract The quality of the Souss-Massa Daraa (S-MD) aquifer is influenced by natural and anthropogenic contaminations. Indeed, geological formations are the main sources of mineralization in the aquifer, which compromises the potential irrigation, and threatens the sustainability of agricultural activities. In this context, hydrochemical and statistical studies were carried out on the major and secondary elements of water, based on different physico-chemical parameters, such as T °C, pH, EC (electric conductivity), NO3- (nitrate), Cl- (chloride), HCO3- (bicarbonate), SO42- (sulfate), Ca2+ (calcium ions), Mg2+ (magnesium ions), K+ (potassium ion), Na+ (sodium), Na%, Mg% and SAR (sodium adsorption ratio). The sampling was carried out in 2018, over two seasons (winter and summer), by analyzing 26 wells distributed over the studied plain. According to the water classification based on EC, it was found that 80% of the samples show very high mineralization, and 96.66% are very hard and unfit for human consumption. Also, Cl- values of most of the samples were within limits inappropriate for irrigation, but some estimated parameters, such as Na% and SAR, were within appropriate levels. In addition, according to the piper diagram, the waters are characterized by a geochemical facies of 86.66% NaCl (sodium chloride), 13.33% CaSO4 (sulphated calcium) and Mg. Thus, the principal component analysis (PCA) shows that the region waters mineralization is of natural origin. Keywords: Souss-Massa Daraa aquifer, hydrogeochemical and statistical studies, Piper and Wilcox’s diagrams, water quality, facies, and agricultural activities.

Abstract Silver (Ag) is considered as an ancient and durable precious metal that is used in different ways, due to its specific properties. The diversity of its uses has been meeting a growing worldwide demand that exceeds the Ag amount extracted from earth crust (primary resource), where a large part of this metal has been exploited. Due to its toxicity, environmental pollution resulting from industrial plants, and high economic value, Ag recovery from industrial plants (second resource) has become increasingly important for scientists. In this study, we focused on Ag recovery from the effluents of mirror industry. This was done by Ag electrodeposition on an aluminum (Al) electrode surface. This work aimed to study the effect of current intensity (CI), electrolysis time (ET), voltage (V) and temperature (T) parameters on Ag electrodeposition, in order to optimize them. According to the obtained results, the optimal parameters were a CI of 4 A, during an ET of 30 min, at 12.5 V, with a maximum T of 30 ºC. Scanning electron microscope (SEM) analyses showed a multilayer rich Ag deposit on the Al surface, followed by a cluster of flowers of different sizes originated from reduced Ag0. Keywords: silver, environmental pollution, Ag recovery, electrolysis and electrodeposition.

Abstract Several engineering mild steel (MS) components have catastrophically failed, due to structural defects, corrosion and wear deformation. These drawbacks have prompted a continuous MS modification, for its higher durability and efficiency. In an attempt to improve the metal performance, Ni–SiO2 (silicon dioxide), Ni–SiO2–C6H5N3 (1H-benzotriazole), Ni–Al2SiO5 (niquel + aluminum silicate) and Ni–Al2SiO5–10C6H5N3 composite films were developed on MS samples, at a constant temperature (T) of 45 ºC, and deposition time of 20 min. The coating performances were investigated by potentiodynamic polarization (PDP) technique, CERT UMT-2 multi-functional tribological testing (MFTT), high resolution optical microscopy (HROM) and high diamond pyramid indentation (HDPI). The samples were further subjected to heat-treatment, and its effects on hardness were examined. PDP study carried out in 0.5 M HCl revealed an improved anti-corrosion resistance. The hardness and wear tests showed better MS mechanical properties. Ni–Al2SiO5–10C6H5N3 coated sample had better hardness and wear resistance features that those from the other samples. HROM unveiled the particles homogeneous distribution throughout MS, with a new surface evolution. MS surface morphology and other properties was optimized by Ni–SiO2, Ni–SiO2–C6H5N3, Ni–Al2SiO5 and Ni–Al2SiO5–10C6H5N3 coatings. Comparatively, NiAl2SiO5–C6H5N3 coated MS exhibited the overall best performance characteristics, and it is thus recommended for advanced applications in petrochemical and marine industries. Keywords: wear, corrosion, MS, hardness and polarization.

Abstract In this study, 2-aminobenzoic acid (ABA) has been used as a complexing ligand for metal ions simultaneous determination by adsorptive cathodic stripping voltammetry (AdCSV). This selective and sensitive method was based on Cu(II), Pb(II) and Cd(II) ions + ABA adsorptive accumulation, by hanging them onto a mercury drop electrode (HMDE), followed by their reduction through differential pulse cathodic stripping voltammetry (DPSCV). Experimental parameters, such as pH, ABA concentration, accumulation time, potential and scan rate, were examined. Under the optimized conditions, linear calibration curves were established for Cu, Pb and Cd concentrations, in the ranges from 5 to 120, 5 to 150 and 5 to 120 ng/mL-1, respectively. Detection limits (LODs) of 2.05, 1.78 and 2.26 ng/mL-1 were obtained for Cu, Pb and Cd, respectively. The proposed method was applied for the determination of these elements in tap and industrial waste water, as real samples. Keywords: copper, lead, cadmium, 2-aminobenzoic acid, AdCSV and water samples.

Abstract In this work, an equi-atomic AlCrFeMnNiV HEA was synthesized by means of arc-melting and casting processes. The casted alloy ingots were heat-treated (annealed) at temperatures of 400, 600 and 800 ºC, for 2 h. The effect of the heat-treatment temperature on the HEA microstructural evolution, compressive strength and corrosion behavior was investigated. Heat-treatment temperatures of 400 and 600 ºC resulted in increased micro-hardness properties that, at 800 ºC, were drastically reduced, although a good combination between strength and ductility was observed. HEA showed an extreme decrease in the current density (J (A/cm2)), after the heat-treatment, with a lower potential (V). The heat-treated HEA demonstrated a good corrosion rate in acidic conditions, as compared to that of nickel (Ni) based, titanium (Ti) alloys and stainless steel (SS) super alloys. Keywords: HEA, AlCrFeMnNiV, arc-melting, casting, heat-treatment (annealing), compression and corrosion.

Abstract A membrane sensor using an ion association complex of hydroxyzine hydrochloride (HDH) with Orange II (ORG-II) dye, in a polyvinyl chloride (PVC) matrix, has been developed and used as a selective electrode for HDH quantification in pharmaceuticals. The sensor is suitable to determine 2.2 × 10-5 - 1.1 × 10-3 mol L-1 HDH, in the pH range from 2.5 to 5.21, with the Nernstian slope of 57.41±1.04 mV/decade, under optimum conditions. The regression coefficient (RC) value of 0.999 shows a good correlation between HDH concentration and the potential measured using the proposed sensor. The sensor limit of detection (LOD) was 4.5 × 10-6 M. A standard-addition procedure was followed to study the effect of various interferents. The results revealed no variations caused by foreign ions or species. The regression equation (RE) and relative standard deviation (RSD) values, from 1.67 to 5, and from 1.86 to 4.81%, respectively, indicated the HDH-ORG sensor acceptable accuracy and precision. The RSD values of ≤5.67 and <5% indicated the sensor acceptable robustness and ruggedness, respectively. It has been successfully used to determine HDH in tablets, and excellent results were obtained. Keywords: HDH, ORG-II, ion-associate, PVC and membrane sensor.

Abstract In this study, gold nanoparticles (AuNPs) were synthesized using sodium borohydride (NaBH4) as reductant. AuNPs size and shape were experimented by using various characterization techniques. The synthesized AuNPs performance capability for atrazine (ATR) detection, at a glassy carbon electrode (GCE), was verified using cyclic voltammetry (CV) as the determining mode. AuNPs impressive electrochemical performance and stability at the GCE led to further studies, without the need to apply nafion. ATR linear concentration plot ranged from 10 to 17 nM, with a lower limit of detection (LOD) of 0.17 nM, and a regression coefficient (R2) of 0.9934, under optimized conditions. The proposed sensor was very reliable, with a relative standard deviation (RSD) of 1.1%, for n = 20, and it was quite sensitive for ATR, with no discernible interference from other ions. Consequently, AuNPs were effectively used to identify ATR in several pesticide industry wastewater samples. Keywords: ATR, AuNPs, GCE, sensor and wastewater.

Abstract Copper (Cu) powder production, in a sulfuric acid (H2SO4) solution with titanium (Ti) ions, was studied by electrolysis, using Cu anodes. It was empirically proven that this process occurs by three different stage-based mechanisms that depend on the electrolyte composition and electrolysis conditions. The first mechanism occurs in a H2SO4 solution with Cu2+ ions and Ti4+ (tetravalent ions). Cu2+ are cathodically reduced, forming Cu powder (CP), since the process occurs at current densities (J) lower than the limiting one. So, part of the current that would be consumed by the hydrogen ions (H+) reduction reaction is spent to reduce Ti4+, which results in Ti3+ (trivalent ions). These, in the cathode space, reduce Cu2+, which, simultaneously, regenerates Ti4+. Then, these diffuse and are again reduced at the cathode, and Ti3+are formed, reducing Cu2+, in a cyclic process that further increases CP production current efficiency (CE) at the near-cathode space, forming more dispersed particles. The second mechanism occurs in a H2SO4 solution with only Ti4+. During the electrochemical circuit current flow, the Cu anode is oxidized to form Cu2+, and Ti4+ are reduced to Ti3+, on the cathode surface. Then, Cu2+ and Ti3+, by diffusing the solution volume and meeting in the inter-electrode space, chemically interact with each other, due to the red-ox (reduction-oxidation) potential difference, forming a dispersed CP and Ti4+. These diffuse one more time, and are again reduced to Ti3+. These processes are cyclically repeated, i.e., Ti4+ work as catalyst. The third mechanism takes place in H2SO4 with Ti3+. When the current flows through the electrolyte, the Cu anode is oxidized, forming Cu2+, which are immediately reduced in the anode by Ti3+, producing CP. Ti4+ are formed due to the red-ox reaction diffusion to the cathode, being reduced to Ti3+on its surface, which again interact with Cu, producing CP on the anode. Since, in all mechanisms (except the first), CP is not directly produced on the cathode surface, but in the inter-electrode space, further growth of Cu particles does not occur. Thus, CP particles of spherical shape, with sizes from 0.01 to 0.1 μm, are formed, with a CE from 95.2 to 99.1%, under optimal conditions. Keywords: ultrafine CP production mechanisms, H2SO4 solution and Ti+ electrolytes.

Abstract Novel sulphur (S)-containing Schiff’s bases, N-((1H-indol-3-yl)methylene)thiazol-2-amine (I3A2AT) and(13E)-N1,N2-bis((thiophene-2-yl)methylene) cyclohexane-1,2-diamine (T2CDACH), were synthesized. The structures were deep-rooted by mass, UV-visible, Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) analyses. The ligands inhibition efficiency (w%) on carbon steel (CS) corrosion in 1 M hydrochloric acid (HCl) was studied using gravimetric analysis, electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation (PDP), electrochemical noise (ECN), quantum chemical and surface studies. Both Schiff’s bases acted as excellent inhibitors on CS corrosion in 1 M HCl. The excellent inhibitors performance was confirmed by the formation of protective adsorption films onto the CS surface. The inhibitors adsorption onto the CS surface followed Langmuir’s adsorption isotherm. Energies of the highest and lowest occupied molecular orbitals (EHOMO and ELUMO), number of electrons transferred (∆N), electronegativity, chemical hardness, and so forth, were evaluated by quantum chemical studies. An acceptable correlation was observed between the results of quantum chemical calculations and other corrosion monitoring techniques. Keywords: adsorption, w%, PDP, quantum chemical approach and S-containing corrosion inhibitors.

Abstract Metals and alloys corrosion is one of the most challenging and damaging occurrence that is linked with enormous economic and safety losses, and it becomes more severe during some manufacturing processes by which metallic surfaces are treated for other industrial application processes. The use of corrosion inhibitors is one of the best way to protect metals and alloys against damage. The problem of the environmental toxicity of some of the employed inhibitors and the high cost involved in controlling and preventing corrosion have prompted this review. Computational chemistry methods are mostly significant in reducing the cost of protecting metals and alloys against corrosion. This review article begins with the summary of the most used computational methods, parameters and, finally, summarizes the results of some studies made by different authors in the field of corrosion science and engineering. Keywords: density functional theory (DFT), Hartree-Fock (H-F), Ab-initio, semi-empirical, acid corrosion, inhibition and alloys.

Abstract The high toxicity of industrial metal corrosion inhibitors raises various environmental and health problems. Thus, the study of metals and alloys corrosion inhibition, in acidic media, by eco-compatible organic compounds, has become a very attractive research field. In this paper, garlic (Allium Sativum) extract inhibition efficiency (IE) against API X60 carbon steel (CS) and 316L stainless steel (SS) corrosion, in a 1 M sulphuric acid (H2SO4) solution, has been investigated using electrochemical techniques, including potentiodynamic polarization (PPD) and electrochemical impedance spectroscopy (EIS). The experimental results showed the remarkable corrosion inhibitive performance of garlic extract (GE). The corrosion IE, which depends on the inhibitor concentration, increased up to 90%, for SS, and 67% for CS, as shown from the PPD tests. EIS analysis showed that the corrosion resistance (CRST) was increased in the medium with GE, indicating the properties improvement of the passive films formed on the steels surfaces. Keywords: corrosion, steel, H2SO4, green inhibitor and GE.