Portugaliae
Electrochimica Acta

[dimOHmIm]+,I- and [dimOHmBim]+,I- were investigated as a corrosion inhibitors for MS in 0.5 M H2SO4 using gravimetric, PDP and EIS techniques. Polarization curves revealed that both compounds acted as mixed-type inhibitors, and that corrosion IE% increased with their higher concentrations. The adsorption of both inhibitors onto the MS surface obeyed Langmuir’s isotherm. The compound II showed a higher corrosion IE% than that of I. The quantum chemical calculations were applied to investigate the relationship between the two azolium salts derivatives electronic properties and their corrosion IE%. Keywords: imidazolium and benzimidazolium salts, MS, polarization, EIS, WL and corrosion inhibition.

Scraped or end-of-life WC-Co bonded makes it an attractive resource. The conventional technologies to recover these metals entail energy-intensive pre-treatment steps, followed by their dissolution in a high volume of concentrated acids/alkali reagents. Recently, much attention has been given to the development of energy-efficient and environmentally friendly routes based on WC-Co direct electrochemical dissolution as anodes. However, the metals have a retarded dissolution, in NaOH alkali media, due to the formation of passive oxide layers, in the acidic electrolytes, and of hydroxides, on the anodic surface. The present study investigated WC and Co dissolution fundamentals in aqueous NH3, in order to develop a greener process, by the suitable addition of (NH4)2CO3, (NH4)2SO4 and NH4Cl Preliminary PDP studies revealed the necessary concentration of NH3 and additives, and their effect on the metals passivation tendency, for obtaining the best anodic dissolution parameters. The electrodissolution experiments in a specially designed cell achieved the maximum values, by adjusting those parameters. The highest dissolution of W and Co occurred under optimum conditions (10 V, 150 g/L NH3 and 15% w/v NH4Cl). Co was deposited at the cathode, while H8N2O4W remained in the electrolyte and was recovered as H2WO4 or YTO. Topographical analysis of the polarized surface by AFM has confirmed the pitting corrosion mechanism responsible for W and Co dissolution. A process flow chart for the newly developed single-step direct recycling methods of WC scraps has also been proposed. This process has produced pure saleable WO3 powder and Co. Keywords: WC-Co scrap, recycling, NH3 electrolyte, PDP, electrodissolution, WO3 and Co.

In this research, ZL leaves extract was used as a new friendly inhibitor for improving CS corrosion resistance in a 1.0 M HCl solution. The extract performance was evaluated by PDP and EIS techniques. The outcomes of this investigation showed that corrosion IE% of ZL leaves C2H5OH extract raised from 86 to 95%, with concentrations from 1 to 3 g/L. EIS method confirmed that the extract IE% was stable in the long-term. However, when the test temperature increased from 293 K to 323 K, IE% decreased from 95 to 90%. PDP experiments results revealed that ZL leaves extract operated as a mixed-type inhibitor, with anodic predominance. Keywords: ZL leaves extract, corrosion, electrochemical techniques, immersion time and carbon steel.

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.