Portugaliae
Electrochimica Acta

The corrosion behavior of Zn-Al-Cu alloy was investigated in HCl solution in absence and in presence of different concentrations of inhibitors. The techniques of measurements were: weight loss, linear polarization and galvanic static polarization. It was found that the corrosion rate of this alloy was higher than that of zinc or aluminum. The inhibitors used were: heterocyclic piperidine (PP), 2- methyl piperidine (2mp), 3-methyl piperidine (3mp) and 4- methyl piperidine (4mp). These inhibitors are mixed type and their inhibition efficiency, I%, increases according to the order: 2mp < 3mp < pp < 4mp. The values of activation energy of corrosion were determined in absence and in presence of inhibitors. It was found that the presence of these inhibitors increases the values of activation energy. The adsorption of these inhibitors on the surface of the alloy follows Frumkin’s isotherm.

The inhibitive effect of the gum exudate from Acacia seyal var. seyal on the corrosion of mild steel in drinking water was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results obtained show that gum exudates could serve as effective inhibitors for the corrosion of steel in drinking water network. The percentage inhibition increases with increasing the concentration of the gum at 30 oC. The percentage inhibitor efficiency above 95 % was attained at gum concentration 400 ppm. The corrosion rates of steel and inhibition efficiencies of the gum exudates obtained from impedance and polarization measurements were in good agreement. Potentiodynamic polarization studies clearly reveal that the gum behaves predominantly as an anodic inhibitor. The study also shows that the inhibition efficiency was insignificantly affected by the temperature rise of the medium.

Exudates gums from Pachylobus edulis (PE) and Raphia hookeri (RH) were evaluated as corrosion inhibitors for aluminium in HCl using weight loss and thermometric measurements at 30 – 60 oC. The exudates were found to retard corrosion rate of aluminium. The inhibition efficiency (%1) increased with increase in concentration of the exudates. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PE and RH exudate gums were found to obey Temkin adsorption isotherm and Kinetic-Thermodynamic Model of El-Awady et al. at all the concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. Exudate gum from RH was found to be a better inhibitor than PE.

This work is a study of 2.5-difuryl-N-methylpyrrole (B1) compound on the corrosion of steel in HCl medium. The investigation was carried out using gravimetric and electrochemical polarisation measurements. The corrosion rate decreases continuously with concentration of the compound (B1) and the efficiency increases to reach 90 % at 10-3 M. Polarisation results indicate that B1 is a cathodic inhibitor. B1 is adsorbed on metal surface according to the Langmuir isotherm. Value of free enthalpy of adsorption obtained involves chemisorption between inhibitor molecules and metal surface.

The influence of heat treatment on the corrosion behavior of two aluminium matrix composites (AA2014/15 vol% Al2O3p - composite A and AA2009/20 vol% SiCw -composite B) was analyzed in 3.5% sodium chloride solution. The kinetic of the corrosion process was studied based on the gravimetric measurements. The corrosion damage and pit shape were analyzed by Image Analyzer. The corrosion damage in both composites was caused by the pitting attack on the surface. Pit shape of the composite A is different to the composite B. The corrosion rate of composite A is higher than composite B because the voids or gap between reinforcement particles and matrix are larger than in the composite B. The main attack of nucleation sites was at the interface region of the matrix and the reinforcement.

The inhibiting action of the calyx extract of Hibiscus sabdariffa on mild steel corrosion in 2 M HCl and 1 M H2SO4 solutions was assessed using a gasometric technique. The results demonstrate that Hibiscus sabdariffa extract suppressed the corrosion reaction in both acid media and inhibition efficiency increased with extract concentration with slightly higher values obtained in 1 M H2SO4. Synergistic effects increased the efficiency of the extract in the presence of halide additives. Adsorption characteristics of the extract were approximated by the Langmuir isotherm. The inhibition mechanisms, estimated from the temperature dependence of inhibition efficiency as well from kinetic and activation parameters show that the extract functioned via mixed-inhibition mechanism. It is suggested that molecular as well as protonated organic species in the extract contribute to the observed inhibiting action.