Portugaliae
Electrochimica Acta

In the present work, an EC used for steel corrosion protection was characterized by Ec techniques. This study aimed to describe the effect of the steel roughness surface on the performance of EC, through EIS and other methods. The studied metal was a low-strength CS immersed in a 3.5% NaCl solution. The CS surface was obtained by polishing it (metal electrodes) with an abrasive paper of 120, 600 and 1200 mesh. Then, the electrodes were painted with an anti-corrosive EC, which contained Zn3 (PO4)2 as an anti-corrosion agent. The study of the influence of the CS surface Ra and its corrosion behaviour and of the evolution of the protective capacity systems on the EC performance was made by stationary (Ecorr and Tafel plot) and no-stationary Ec techniques (EIS and CA). In order to confirm the detachment and blistering on the coating, the coated CS samples were analyzed by a salt spray in a 7.69 % NaCl solution, with an IT of 15 days. The obtained results showed that the CS surface state directly influenced the coating performance and the Ec parameter values variation, as a function of IT in the NaCl solution. EIS was the most valid Ec method for the studied coatings. Keywords: corrosion; CA; EIS; EC; surface roughness; Tafel plot.

Al and its alloys have a low atomic weight and high strength to density ratio. These properties make them very useful for the construction of parts in automotive industry, such as engine blocks or pistons. Al is prone to corrosion, due to its negative standard E of 1.66 V vs. NHE. In addition, Al corrosion resistance strongly depends on pH. Therefore, it is important to undertake a general study of Al corrosion behavior. Keywords: Al; CI; corrosion; electrochemical behavior; oxides.

A novel p(THFA-co-HEMA) membrane based on acrylate CP was successfully synthesized through PP technique, and applied into Pb-ISE (Pb-ISE). THFA optimum composition was HEMA 9:1 (TH91), with a Tg of -6.5 oC. The structure of p(THFA-co-HEMA) was characterized using FTIR. The Pb-ISE sensor showed remarkable calibration measurement in the range from 0.1 to 10-6 M, with a LOD of 7.59 x 10-7 M, and it has obeyed a Nernstian number of 30.5 mV/dec. In addition, the fabricated Pb-ISE sensors showed fairly good selectivity coefficients of several types of ions, such as K+ (-6.53 ± 0.11), Na+ (-6.35 ± 0.16), NH4+ (- 6.76 ± 0.11), Mg2+ (-12.15 ± 0.13), Ca2+(12.12 ± 0.14), Cu2+ (-4.33 ± 0.11) and Cd2+ (-6.43 ± 0.17), and an effective function in the pH range from 3 to 8. The resulting response time was quite good, 6.7 sec, with a change of 27.5 mV for a decade. The Pb-ISE sensor also showed validation results equivalent to AAS standard method, where the corresponding data with real samples produced values of 9.3 ± 1.9 and 9.2 ± 2.0 ppm and 275.5 ± 10.3 and 277.7 ± 4.0 g/g, for CREW and CRMS, respectively. Keywords: acrylate membrane; ISE; p(THFA-co-HEMA); Pb(II); PP.

MS corrosion behavior was herein studied via green azo methane, i.e., BDTT, in a 0.5 M H2SO4 solution. CI mechanisms were investigated by Ec techniques (PDP, EIS and WL). Experimental studies results were supplemented with theoretical calculations, DFT and various Td adsorption and activation parameters. BDTT molecule mechanism of adsorption onto the MS surface followed Langmuir’s isotherm. In this study, an eco-friendly and cost-effective strategy to hinder corrosion was proposed. Keywords: BDTT; CI; DFT; EIS; PDP; WL.

PA is a gram-negative pathogen that is highly aggressive and known to cause several nosocomial infections, leading to significant morbidity and mortality levels. Individuals with compromised immunity are especially vulnerable to life-threatening infections caused by this bacterium. PA importance as a pathogen is further underscored by its virulence, increasing resistance to antibiotics, and its ability to adapt to diverse environmental conditions. In this study, MO extract antibacterial activity was evaluated using Ec methods, such as CV, EIS and polarization curves (Tafel’s law), against pathogenic bacteria, including PA. The performance of the developed CPE modified by MO was herein tested with C6H12O6, by CV technique. The CV recorded at the CPE-MO surface showed a well-defined peak, which was due to C₆H₁₂O₆ Ec oxidation. PA addition to the electrolyte solution containing C₆H₁₂O₆ caused its oxidation peak to disappear. The hypothesis that PA would adhere to the CPE-MO surface, blocking the active sites and, subsequently, C₆H₁₂O₆ oxidation, was proposed. To verify this hypothesis, polarization curves and EIS, which revealed the presence of a non-conductive film on the CPE-MO surface, were employed. The morphology of the elaborated electrodes surfaces was characterized by SEM. Keywords: CPE; CV; EIS; inhibition; MO; PA; pathogenic bacteria; polarization curve (Tafel’s law); SEM; SR.

MS surface deterioration is one of the most challenging problems, since it can be exacerbated by several industrial processes, such as descaling and pickling. In the proposed investigation, chemical and electrochemical techniques determined COLE IE(%) on MS corrosion in a 1 M HCl medium. COLE contains many Pc responsible for an excellent IE(%), since it forms a coating that adsorbs onto the metal surface and shields it from corrosion. Tafel polarization curves outcomes demonstrated that COLE is a mixed kind of CI. According to EIS measurements, Rct rose as Ct of COLE was increased. The relationship between T and MS corrosion behaviour in 1 M HCl with COLE addition was investigated from 300 to 320±1 K. G, which was determined from Langmuir’s isotherm model, revealed that COLE molecules predominantly blocked HCl attack by mixed physisorption and chemisorption mechanisms. Surface morphology studies validated electrochemical and chemical findings by FT-IR, SEM and WCA techniques. Furthermore, DFT computations demonstrated COLE effective interfacial adsorption onto the MS surface. Keywords: 1 M HCl; CI; COLE; DFT; EIS; FT-IR; MS; SEM; WCA.

This work presents a set of electrochemical techniques applied to investigate the effect of Zn baths with additives on steel surfaces coating by EP. The form and intensity of the reduction in I were analyzed as a function of the applied E, using LSV. In this way, different stages of the EP process involved in Zn deposition on steel surfaces, and the effect of each additive, were identified. First, commercial additives produced by a local company, with highly complex compositions, were studied to understand their Ct effects on the different stages of steel coating in Zn baths by the EP process. Based on the ability to replicate those results, C7H6O2 and Triton X-100, previously reported as brightener and leveler, respectively, were proposed as a simple additive mix. Very strong synergetic effects were present, even in this simplified bath. The effect of different additives Ct on the steel coatings grain size or morphology was also evaluated using SEM images, in the final stage. A correspondence between optimal Ct of the commercial additives (1 x 10-2 M Triton X-100 and 3 x 10-9 M C7H6O2) and the proposed bath was found. Finally, EIS experiments were carried out for the different bath compositions, with this simplified additive mix. The results were interpreted through an equivalent electrical circuit represented by Rct, with two parallel CPE, which evidenced Zn deposits inhomogeneities. Keywords: additives in ED; C7H6O2 commercial mix; chemical speciation; EIS; EP process; LSV; SEM; Triton X-100; Zn coating.

The present study demonstrated that, when a Cu-Ti electrode pair was polarized in an aqueous SO42- electrolyte, Cu was oxidized to a divalent state, under AC. In the solution volume, Cu2+ interacted with OH¯, to produce Cu(OH)2. Depending on the electrolysis conditions, Cu(OH)2 underwent a dehydration reaction, which produced CuO. Under industrial AC, each electrode was alternately polarized, firstly towards the anode, then to the cathode. CuE passivation did not occur. With a change in j on TiE, in the range from 0 to 75 kA/m2, CuE dissolution CE increased, reaching 96.5%. When j on CuE was increased to 1000 A/m2, Cu dissolution CE was above 90%. The most favourable conditions for CuE dissolution were a Na2SO4 Ct from 65 to 75 g/L, experiment duration of 1 h, room T, and I frequency of 50 Hz. The obtained CuO (II) composition was identified by XRD and EDXRF analyses. Keywords: AC; Cu; CV; dissolution; electrolysis; Ti.

BM is a renewable organic material obtained from plants and animals. The inability to characterize BM samples prior to the Py process reduces B-O yield quality. This study performed woody (IS and MB) and non-woody (CS and EG) BM samples preliminary characterization, to evaluate their energy potential in Py processing, for improving B-O yield quality. BM samples were sourced from Omu-Aran, Kwara State, Nigeria (latitude 8°08ʹ18.85ʺN and longitude 5°06ʹ9.36ʺE), and were subjected to Pc, structural compositional and thermal analyses. Results showed that all BM samples had good energy potential performance for B-O yield good quality. However, CS had the lowest AC (3.36%) and MC (0.4%), which are favorable properties that enhanced B-O yield quality. The highest AC (5.90%) recorded for EG shows that it had the lowest calorific value, which enabled the release of harmful substances into the reactor, during Py experimentation. Keywords: BM; characterization; proximate analysis; RE; TGA; ultimate analysis.

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.