Portugaliae
Electrochimica Acta

Abstract Silver is widely used in various industries, which makes it highly demanded. Presently, 20% of the world’s silver production originates from naturally occurring Ag mines, with the remaining 80% coming from the Earth’s crust, as a byproduct of the production of Cu, Zn and Pb mines. In this study, using a simple stirred reactor, Ag could be recovered by cementation onto Zn from its monometallic and mixed metal nitrate solutions, as well as from waste X-ray films. The recovery of Ag from its monometallic solution increased with higher molar ratios of Zn to Ag, rotational speed and temperature, while the percentage recovery of Ag decreased with increasing acidity. For the sequential recovery of metals from a mixed metal solution, the migration velocities of the cations determined the order in which they were separated. The recovery of Ag from spent X-ray films could be achieved with a purity of 98.3% by mass. Keywords: Ag recovery; cementation; migration velocity; sequential recovery; waste x-ray films.

ATK was investigated to ascertain its IE(%) on ASTM A36 MS corrosion in a HCl medium. This was possible through the use of WL, Td, Tm, PDP, EIS and SEM techniques. It was seen from all experimental results that, through adsorption onto the MS surface, ATK mitigated active corrosion sites. CR was seen to decrease with higher inhibitor Ct from 197.6 to 19.3 mg/hr-1/cm2. IE(%) of ATK, which rose from 50 to 90.2%, with corresponding increased Ct, from 150 to 750 ppm, was better by adding PPQ to it than ATS. An increase in Rct, up from 346 to 1153 Ω/cm2, and a decrease in icorr, from 312.2 to 64.4 mA, were seen, with higher Ct of ATK, which indicated reduced anodic dissolution and better CI. A mixed type inhibition was deduced from Tafel slopes of PDP results. A physical adsorption mechanism was proposed, while, in Td terms, ATK exhibited a stable and spontaneous reaction. Keywords: ASTM A36 MS; ATK; ATS; corrosion; computational and electrochemical studies; EIS; PDP; PPQ: SEM.

IE(%) of SCLAE on CR of CS immersed in 1 N HCl was herein assessed by WL method. The former increased and the latter decreased in the solution with higher Ct of SCLAE. The inhibitor blocked MS corrosion active sites, and created a protective layer that covered its surface. Pc constituents of SCLAE allowed the interaction between their hetero atoms and the metal ions from the CS surface, hindering its corrosion. Elc studies were herein used to confirm the formation of a protective layer on the CS surface. They were further reinforced by surface analysis techniques, such as FTIR and SEM. EDAX was used to analyze the elements present on the CS surface, after its immersion in 1 N HCl without and with SCLAE. Ra of polished, corroded and inhibited CS surfaces was analyzed by SEM and AFM. Keywords: AFM, corrosion, CS, EDAX, FTIR, HCl, IE (%), SCLAE, SEM and WL method.

In view of enhanced Pc applications, doped materials have drawn much attention. The present work focused on synthesizing pure and Pd doped WO3 Np, which were used as Pc for MB and RhB aqueous solutions discoloration, under VL, by a unique MWI technique. XRD and TEM studies revealed that Pd dopant did not influence WO3 samples structure and morphology, since they had mono-dispersed spherical forms, with an average diameter of about 50-30 nm. Optical spectra showed a red shift in the absorption edges, with an increase in Ct of Pd from 0 to 10 wt%, which indicates the decrease in Eg of WO3 with Pd doping. Eg was calculated as 3.02, 2.84 and 2.73 eV, for pure and Pd (5 and 10 wt%) doped WO3 samples, respectively. Pc intensity of Pd doped WO3 was significantly higher than that of the pure one. This was due to the recombination of photo-excited electrons and holes. Pc activities of pure and Pd doped WO3 samples were analyzed based on their ability to degrade MB and RhB dyes under VL. Pd doped WO3 showed better Pc degradation, due to an increase in SA, and a decrease in Eg and O vacancies. Keywords: MWI; Pc; Pd; TEM; WO3; VL; XRD.

This study carried out Bg anaerobic Cd. RSM was employed to investigate optimum experimental conditions for Bg yield. Input parameters were PD substrates combination, either with WH or GS. Using six different identical 25 L cylindrical digesters, 6 substrate combinations experimental setups were carried out, for an incubation time of 22 days, under ambient T of 33 °C and pH of 6.7. The setups digesters were: 25% PD:75% WH (1); 50% PD: 50% WH (2); 75% PD:25% WH (3); 25% PD:75% GS (4); 50% PD: 50% GS (5); and 75% PD:25% GS (6). From experimental observations, Bg yield started on day 5, for setups 1, 2, 4 and 5, followed by setup 3 on day 6. Setup 6 was the last digester to produce Bg, on day 7. Setup 2 recorded the highest Bg yield (75 cm3/day), while setup 6 had the lowest value yield (48 cm3/day). Furthermore, additional setups (7 and 8) were carried out for determining Bg characteristics, and evaluating the effect of a pre-activated active slurry on its yields. Optimum Bg yield (75 cm3/day) was attained by 50% PD: 50% WH. This result validates Bg production through substrates Cd, and the employment of optimization tools, in order to obtain ideal process parameters. Furthermore, quadratic model developed by RSM was highly reliable and reproducible, while the predicted values were close to the experimental ones. Keywords: AD; additives; Bg; Cd; optimization; RSM.

This study performed LSV simulation of two-step irreversible electron oxidation with the intermediate (E↓E), which was immobilized on the electrode surface. The response exhibited either one or two peaks, depending on the intermediate stability. The first electron transfer depended on the reactant diffusion, while the second one was a function of the accumulated intermediate. For this reason, the second Ip was higher than the first one, and the single peak split into two peaks, under the influence of an increased SR. Thermodynamic and kinetic parameters influence on the two components of the response were analyzed. Keywords: EE mechanism; intermediate immobilization; kinetic stabilization; two-step electron oxidation; voltammetry.

Abstract Adsorption behavior of Ca particles obtained from SS, PS and ES calcination, as well as its Td parameters, during A36 MS coating via phosphating process, was investigated. A36 MS coupons surfaces were coated with phosphates and varied C of Ca particles (from 1 to 2.5 g/dm3), at a T of 60 and 80 ºC. Ca particles (as inhibitor) adsorption onto the MS surface obeyed Freundlich’s isotherm, with R2 values around 1. Kads and Td parameters, such as ∆G, ΔH and ΔS, were also determined. A36 MS coated with Ca particles obtained from calcined SS gave the best A capacity, as revealed in terms of Kads, ∆G and ∆S values. Higher Kads was obtained when T increased from 60 to 80 ºC. Also, Td parameters results revealed that Ca particles adsorption mechanism on MS was a more spontaneous process, at an increased T of 80 ºC. Keywords: adsorption; Ca particles; corrosion; MS; Td.

Abstract This study researched S275JR MS corrosion sites deactivation in [Na3H(CO3)2] heavy deposits (Gamboru, Borno State, Nigeria), using PPQ as alternative inhibitor, and employed WL, HER, EIS, PDP, SEM and computational techniques. PPQ showed effective MS corrosion mitigation in [Na3H(CO3)2] heavy deposits. IE(%) of 98.8, 99.5, 82.9 and 95.9 %, for gravimetric, HER, EIS and PDP, respectively, at 208 K, were obtained. PPQ had a shortest E of 0.1 eV, with a higher absolute molecular σ of 2.4, compared to molecular η of 0.4, which makes it a better inhibitor of MS corrosion in [Na3H(CO3)2] heavy deposits. With higher inhibitor Ct, its IE(%) increase and CR of MS decreased. This was due to PPQ molecules strong adsorption onto the MS surface. PPQ was also thermodynamically stable, showed less disorderliness, and its absorption was spontaneous and physical. Keywords: adsorption; corrosion; EIS; HOMO; LUMO; [Na3H(CO3)2]; physisorption PDP; PPQ; SEM.

Abstract The word corrosion has been a major issue in the industry, especially in industrial infrastructures, such as steel materials, causing great losses in revenues and environmental pollution. This research goal was to contribute to solving the aforementioned issues. CP as CI, on TS samples in 0.5 M HCl and 0.25 M H2SO4 media, was studied via electrochemical, FTIR and OM techniques. All the results proved the presence of active components in CP, which mitigated TS samples corrosion in the corrosive media. CR reduced greatly for all the TS samples, as CP IE(%) increased. Also, OCP showed that CP operated with mixed adsorption mechanisms. FTIR analysis revealed the numerous functional groups that enabled CP IE(%), by retarding TS samples corrosion. OM images showed the corrosion damage on TS samples without CP, and the film coverage on the alloy, after the inhibitor addition. This confirms CP excellent adsorption onto TS samples. Keywords: active components; CI; CR, functional groups; FTIR; OM.

Abstract Corrosion is a major challenge faced in industries, which has to be addressed by using inhibitors. The aim of this study was to investigate ESE as CI of MS in a 30 wt% NaCl solution. ESE was subjected to Pc analysis, to identify the presence of active ingredients that would create a good CI. CI of ESE at different C was investigated using WL, PDP, SEM, FTIR and EDXS techniques, to characterize MS samples. The best process level from the experimental design was observed at T of 24.4 ºC, IT of 6 days and ESE C of 0.4 g/L, with IE(%) of 95.5%. The presence of metabolites in ESE was confirmed by Pc analysis, which suggested the extract was a good CI. Results from PDP and WL techniques were in good agreement. SEM, FTIR and EDS data revealed that the optimal procedure level produced a stronger protective film on the MS surface. It was concluded that ESE acted as a good and environmentally friendly CI. Keywords: CR; EDXS; FTIR; IE(%); optimization; PDP; SEM; WL.

Abstract The application of inhibitors against metals and alloys corrosion in various aggressive environments is an excellent solution. The present study explored Cu corrosion inhibition in a 0.5 M H2SO4 solution by MP EO, from Western Morocco, using EIS and PDP analyses. GC coupled with MS revealed that MP EO is mainly composed of pulegone (23.38%), isomenthone (20.54%) and l-menthone (9.56%). MP inhibitory behavior was of mixed type. MO EO prevented Cu corrosion in H2SO4, with an IE(%) that increased with its Ct, at a maximum of 91.0%, with 1 g/L. The Cu surface was studied by SEM coupled with EDS. Keywords: Cu, EDS, EIS, EO, GC, H2SO4, IE(%), MP, MS and SEM.

Gravimetric, electrochemical, surface investigation, RSM and theoretical computational studies, using DFT and MD, were employed to investigate Ecorr inhibition of MS surfaces in 0.5 M H2SO4, by a worm expelling drug (Wormin® MBZ). The results from computational and RSM optimization and experimental methodologies were all in good accord. After 24 h, IE(%) of 1.5 g/L MBZ on MS corrosion, calculated from WL data, was 96.610%. Maximum IE(%) of 1.0 g MBZ was 96.903% (303 K) and 99.998% (333 K). PDP confirmed MBZ mixed nature of adsorption. The impact of the inhibitor C and IT of MS on IE(%) of MBZ was revealed by statistical evaluation and optimization, using Design Expert software package (Stat-Ease). The optimized IE(%) of 96.6103% was obtained with the inhibitor C of 1.061 g/L, at MS 48.58 h IT. On the MS surface, MBZ behaved according to Langmuir’s adsorption isotherm. MD showed that MBZ had an Einteraction of -536.33 and -694.53 kcal/mol, at 303 and 333 K, respectively. Negative Einteraction forecasts confirmed MBZ-MS surface interaction capability, which reinforced the experimental investigations IE(%) findings. Keywords: adsorption; C7H6N2 derivative; DFT; MBZ; MD optimization; RSM; PDP.

Abstract MS is extensively used in oil and gas industries, but its inherent susceptibility to corrosive attack in marine environments with high C of Cl- is a shortcoming to its applications in such inevitable medium. Coating has been a popular means of mitigating steel structures corrosion. This work assessed the effect of Zn-ZnO based AW-SS composite as AC material on a MS substrate in a marine environment. The Zn-ZnO base was separately subject to CD with SS, DLFA and LSLA particulates on MS substrates. PDP method was used to ascertain corrosion behaviors of the coated samples in a simulated SW environment. The samples  and microstructural properties were studied by a microhardness tester and SEM, respectively. The results indicated that the samples  increased when they were coated by SS and LSLA higher C, which had the highest and lowest , respectively. The coatings CP improved visibly with SS, which had the highest value (61.4%), followed by DLFA (53.8%) and LSLA (44.3%). AW incorporated into Zn-ZnO is a potential AC material. Keywords: AW; CI; coatings; ED; environment; MS.

Abstract Metals can contaminate the environment and increasingly affect ecological systems and public health worldwide. Cu(II) and Pb(II) ions play a significant part in increasing the cancer rate, since their amounts are higher in cancerous patients than in healthy individuals. Electrochemical methods have been extensively used for analyzing biological, beverages and food samples to estimate Cu(II) and Pb(II). The present study has employed LSASV for Cu(II) and Pb(II) determination in female patients (suffering from breast-cancer) cancerous blood serum samples. Optimized conditions for analysis have required: Gc, with an eacc of -0.2 V and a tacc of 400 s, as WE; 0.1 M AB (pH 5.1) as SE, at a stirring rate of 9 rpm and SR of 100 mV/s-1; Ag/AgCl as RE; and a Pt wire as CE. Under the optimized conditions, the cost-effective procedure was successfully applied for Cu(II) and Pb(II) determination in cancerous human serum. LOD was in the range of ppb. The analysis indicated higher Cu(II) and Pb(II) levels in cancerous female patients than in the healthy ones. Therefore, a strictly controlled diet is recommended. Keywords: biological sample; Cu(II); healthy and cancerous serums; LSASV; Pb(II); public health.

Abstract The effective inhibition of MS corrosion in H2SO4 by CP and CP + KI was assessed by EIS. SM of MS was studied using SEM and AFM. The rise in Rct and decrease in Cdl, with higher C of CP and CP + KI, confirmed MS CI. IE(%) increased with higher C of CP only and CP + KI (from 10-3 to 10-1 M). CP maximum IE(%) was 93.9%, at 10-1 M. CP + KI, due to I- ions synergistic effect, showed an IE(%) of about 98.8%, at 10-1 M. CP only and CP + KI adsorption mechanism followed Langmuir’s isotherm. SM studies suggested that a barrier film of CP only and CP + KI, mitigated MS surface corrosion. CP + KI is an efficient inhibitor in H2SO4. Keywords: AFM; corrosion; CP; EIS; IE(%); KI; MS; SM; SEM.

Abstract A potentiostat is a device that enables to measure I that flows through one of the electrodes, by imposing a E. It was invented in 1942, by Hickling. Potentiostats available on the market offer a wide variety of functions. Unfortunately, their prices are high, which is mainly due to a sophistication that is not necessary for experiments such as those practiced at the undergraduate level. Therefore, this paper proposes the fabrication of a multi-channel potentiostat that is inexpensive, interdisciplinary, and enables to plot, for several Ec cells, a certain number of curves describing the evolution of the measured electrical quantities. Specifically, it allows to measure Icorr and analyze the solution chemical reactivity. Keywords: Al corrosion; Ec; electronic materials; potentiostat.

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.