Portugaliae
Electrochimica Acta

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.