Inhibitory action of aqueous coffee ground extracts on the corrosion of carbon steel in HCl solution

The effects of aqueous extracts of spent coffee grounds on the corrosion of carbon steel in a 1 mol L⁻¹ HCl were examined. Two methods of extraction were studied: decoction and infusion. The inhibition efficiency of C-steel in 1 mol L⁻¹ HCl increased as the extract concentration and temperature increased. The coffee extracts acted as a mixed-type inhibitor with predominant cathodic effectiveness. In this study, the adsorption process of components of spent coffee grounds extracts obeyed the Langmuir adsorption isotherm. The chlorogenic acids isolated do not seem to explain the corrosion inhibition observed during the use of the coffee extracts.     

Sodium molybdate as a corrosion inhibitor for aluminium in H3PO4 solution

The inhibition effect of sodium molybdate (Na₂MoO₄) on the corrosion of aluminium in 1.0 M H₃PO₄ solution was studied by weight loss, potentiodynamic polarisation curves and electrochemical impedance spectroscopy (EIS) methods. The results show that Na₂MoO₄ is a good inhibitor, and the inhibition efficiency obtained by three methods is higher than 84% at 20 mM. The adsorption of Na₂MoO₄ obeys Freundlich isotherm at lower concentrations (1–7 mM), while Langmuir isotherm at higher concentrations (7–20 mM). Polarisation curves indicate that Na₂MoO₄ acts as an anodic inhibitor. EIS spectra exhibit three loops (two capacitive loops and one inductive loop).     

Interpretation of the corrosion process of a galvannealed coating layer on dual-phase steel

The dissolution process of a galvannealed coating layer on dual-phase steel was examined by correlating a stripping test, metallographic observations and a polarisation test in an acidified chloride solution. The galvannealed coating layer was composed of several Fe–Zn intermetallic phases, namely the gamma, delta, and zeta phases, from the substrate. The dissolution began from the outermost zeta phase and proceeded to the gamma and then the delta phase. The dissolution rates for each intermetallic phase and galvanic couples were measured and estimated through a polarisation test, and the gamma phase in the gamma-substrate galvanic couple exhibited the highest corrosion rate.     

Responsive behaviour of galvanic anodes in concrete and the basis for its utilisation

In this study, a unique concrete specimen was used to analyse the response of embedded sacrificial zinc and steel anodes to rainfall and fluctuations in temperature. Current from the zinc and steel anodes increased when the environment was aggressive, showing that the required protection current depends on the present level of corrosion risk. A basis for using the ‘responsive behaviour’ of galvanic anodes is provided by the protective effects of pit re-alkalisation and pH maintenance. By contrast, protection based on achieving adequate polarisation inhibits the use of responsive behaviour and galvanic anodes might only deliver adequate polarisation in aggressive environments.     

In situ impedance spectroscopy study of the electrochemical corrosion of Ti and Ti–6Al–4V in simulated body fluid at 25 °C and 37 °C

The corrosion resistance of Ti and Ti–6Al–4V was investigated through electrochemical impedance spectroscopy, EIS, potentiodynamic polarisation curves and UV–Vis spectrophotometry. The tests were done in Hank solution at 25 °C and 37 °C. The EIS measurements were done at the open circuit potential at specific immersion times. An increase of the resistance as a function of the immersion time was observed, for Ti (at 25 °C and 37 °C), and for Ti–6Al–4V (at 25 °C), which was interpreted as the formation and growth of a passive film on the metallic surfaces.     

Inhibiting effect of 2-mercaptobenzimidazole on the corrosion of Cu-30Ni alloy in aerated 3% NaCl in presence of ammonia

The inhibiting effect of 2-mercaptobenzimidazole (MBI) against Cu-30Ni alloy corrosion in aerated 3% NaCl polluted by ammonia, has been developed. Potentiodynamic and electrochemical impedance spectroscopy (EIS) measurements have been applied to determine the corrosion rate. scanning electron microscopy (SEM) studied surface morphology has been used to characterise electrode surface. The obtained results indicate that MBI acts as a good mixed-type inhibitor retarding the anodic and cathodic reactions. An increase of MBI concentration leads to a decrease of corrosion rate and inhibition efficiency increase.     

Pulse reverse plating of Ni-Co alloys: Deposition kinetics of Watts, sulfamate and chloride electrolytes

Fundamental electrochemical properties of electrolyte systems are the prerequisite for the development of a successful pulse deposition process. Three different electrolyte systems for the galvanic deposition of nickel cobalt alloys (chloride, Watts and sulfamate type) were investigated in order to reveal underlying deposition mechanisms and rate determining factors. The electrochemical experiments were supported by X-ray fluorescence analyses of the alloy composition in dependence on the current density and the type of bath. A special focus was set on the investigation of the passive (oxide) layer formation by the anodic pulses.The choice of electrolyte system strongly influences the reaction mechanism and thus the alloy deposition. Also the cobalt content within the deposited layer varied strongly in dependence on the electrolyte system used. While sulfamate and Watts baths show an ability for passive layer formation, the chloride bath exhibits a lower proneness to passivation, accompanied by pit formation     

Corrosion inhibition of carbon steel in hydrochloric acid solution using pomegranate leave extracts

The inhibitive action and adsorption behaviour of pomegranate leave extract (PGLE) on corrosion of carbon steel in 1M HCl solution at 293–333?K was investigated through chemical (weight loss measurements), electrochemical (potentiodynamic polarisation) and surface analysis [Fourier transform infrared (FTIR) and X-ray diffraction (XRD)] methods. Results obtained shows that the adsorption of PGLE molecules on the C steel surface obeyed the Langmuir adsorption isotherm and acts as mixed type inhibitor for C steel in 1M HCl with anodic as its dominant inhibitor at high concentration. The inhibitory property of the extract was discussed in terms of the mechanism by which its components adsorb onto the C steel surface. Activation energy of corrosion and other thermodynamic parameters such as standard free energy, standard enthalpy and standard entropy of the adsorption process as well as FTIR and XRD examinations of the electrode surface revealed that the corrosion inhibition of C steel in 1M HCl in the presence of PGLE is mainly controlled by the physical adsorption process.     

Limitations in the use of the potentiodynamic polarisation curves to investigate the effect of Zn on the corrosion behaviour of as-extruded Mg–Zn binary alloy

The effects of Zn on corrosion behaviour of as-extruded Mg-(1-4)Zn alloys were investigated using an immersion test, a zero resistance ammeter technique, and a potentiodynamic polarisation test. As a result, it was revealed that the solutionised Zn enhanced protectiveness of the passive film, and accelerated the H₂ evolution rate of the Mg–Zn binary alloys. The acceleration of the H₂ evolution rate by addition of Zn leads to an increase in the net corrosion rate of the Mg–Zn alloy. In this research, the polarisation test was found to have some limitations for evaluating the true corrosion behaviour of passive Mg–Zn alloy.     

Improvement of the electrochemical properties of novel solid oxide fuel cell anodes, La0.75Sr0.25Cr0.5Mn0.5O3−δ and La4Sr8Ti11Mn0.5Ga0.5O37.5−δ, using Cu-YSZ-based cermets

A Cu-metal-based cermet was used to improve the electrochemical properties of two novel oxide-based systems with intrinsic low electronic conductivity such as La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCM) and La₄Sr₈Ti₁₁Mn_0.5Ga_0.5O_37.5−δ (LSTMG). The introduction of Cu results in a marked improvement of the polarisation resistance values and hence in the performance. The best results correspond to the addition of ∼15% of CuO. In both systems, the polarisation resistances were improved by a least a factor of 2. Despite there are reports claiming that the CuO-zirconia-based systems exhibit catalytic activity, such an improvement seems to be mainly related to the capability of CuO as a sintering agent, helping to bridge electrode particles together, creating new electronic paths and thus effectively increasing the triple phase boundary through the whole electrode material.