Portugaliae Electrochimica Acta

Role of Halides on the Passivation of Iron in Alkaline Buffer Solutions

Cyclic voltammetric studies were carried out on pure iron in alkaline borate and phosphate buffer solutions at pH 10.8. At higher potentials, on anodic polarization, iron forms FeB4O7 and FeOOH in borate buffer, and FeHPO4 in phosphate buffer which got converted to higher valency phosphates. In phosphate solutions, in presence of halides, the interfacial diffusion layer turned to be cation selective outer sublayer and an anion selective inner sublayer, and in borate solutions a precipitate layer of metal oxyhydroxide was formed, which was anion selective, and anions adsorb on this.

State of Corrosion of Rebars Embedded in Mortar Specimens After an Electrochemical Chloride Removal

El presente trabajo intenta determinar las mejores condiciones a las cuales se puede aplicar una extracción electroquímica de cloruros (EEC) en probetas de mortero de cemento con adiciones de cloruros, monitoreando la velocidad de corrosión antes, durante y después de la aplicación de la EEC. La EEC fue aplicada a diferentes condiciones: a) densidad de corriente (1 y 2 A/m2 en relación a la superficie del acero), b) tiempos de aplicación de la técnica (15, 30 y 60 días), y c) con distintos grados de precorrosión en las varillas de acero. De acuerdo a los resultados obtenidos, se puede decir que si la EEC es aplicada preventivamente, la técnica puede resultar eficiente para detener la velocidad de corrosión de las barras de acero. Sin embargo, si es aplicada demasiado tarde no se puede asegurar la repasivación de las estructuras. La eficacia de la EEC depende en gran medida del tiempo de aplicación y del grado de precorrosión que presenten las barras de acero.

This work attempts to determine the best conditions for applying the Electrochemical Chloride Removal (ECR) in rebars embedded in cement mortar with chloride additions by monitoring the corrosion rates before, during and after the application of an ECR. The ECR was applied at different conditions of current density (1 and 2 A/m² of steel surface), application times (15, 30 and 60 days) and degree of precorrosion of the rebars. According to the results obtained, if ECR is applied preventively, it is an efficient procedure for delaying the start of corrosion. However, if applied too late, it does not assure the repassivation of corroded reinforced concrete structures and is therefore useless. The efficiency of the ECR depends heavily on the application time and the degree of precorrosion of the rebars.

Testing Natural Fenugreek as an Ecofriendly Inhibitor for Steel Corrosion in 1 M HCl

The influence of a natural extract of fenugreek on the corrosion of steel in 1 M HCl has been studied by weight loss, polarisation and EIS measurements. Results obtained show that the natural substance inhibits the corrosion process. It acts on the cathodic domain without modifying the reduction mechanism. The inhibition efficiency increases with fenugreek concentration to attain 94% at extract of 10 g/L of fenugreek at temperatures between 308 and 353K. It is an efficient inhibitor. The effect of temperature on the corrosion behaviour of steel indicated that inhibition efficiency is temperature-independent. The activation energy of adsorption is determined.

Studies on Corrosion of Annealed and Aged 18 Ni 250 Grade Maraging Steel in Sulphuric Acid Medium

The corrosion behavior of aged and annealed sample of 18 Ni 250 grade maraging steel was investigated in varied conditions of concentration and temperature of sulphuric acid medium, using electrochemical techniques like Tafel polarization and electrochemical impedance spectroscopy (EIS). The results obtained from both the techniques are in good agreement. These results have shown increase in corrosion rate of aged specimen with increase in concentration and temperature of sulphuric acid. With increase in concentration of sulphuric acid from 0.025 M to 0.25 M the corrosion rate of annealed sample was found to increase, but there after in 0.5 M, 0.75 M and 1 M, the rate of corrosion decreases, indicating passivation of alloy surface at higher concentration of sulphuric acid. The corrosion rate of aged specimen was found to be higher than that of the annealed specimen. Similar observations are revealed by SEM images. The thermodynamic parameters like activation energy, enthalpy of activation and entropy of activation were calculated.

Study on the Inhibition of Mild Steel Corrosion by Benzoisoxazole and Benzopyrazole Derivatives in H₂SO₄ Medium

Four heterocyclic compounds, namely 4- phenyl-5-acetyl/carbethoxy-3-methyl-6-hydroxyl-6-methyl-4,5,6,7-tetrahydro-2,1-benzoisoxazole and benzopyrazole (BIS1, BP1and BIS2, BP2), were synthesized and their influence on the inhibition of corrosion of mild steel in 1 M H2SO4 was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance (EIS) and scanning electron microscopy (SEM). The values of activation energy and free energy of adsorption of these compounds were also calculated. Adsorption obeys Langmuir adsorption isotherm. The IE of the compounds was found to vary with concentration and temperature. Synergistic effect was also investigated for the four compounds at 0.05 mM concentration by weight loss method in 1 M H2SO4 medium in presence of KI, KBr and KCl. Results obtained revealed that all the four compounds performed excellently as a corrosion inhibitor for mild steel in 1 M H2S0(4) and their efficiency attains more than 90% at 0.6 mM at 298 K. Polarisation studies showed them to be mixed type inhibitors.

Use of Experimental Designs to Evaluate the Influence of 2-Mercaptobenzimidazole on the Corrosion of Mild Steel in HCl (1 M) Environment in the Presence of Alcohol Ethoxylate

The present study attempted to investigate the best conditions for the use of a mixture of 2-mercaptobenzimidazole and alcohol ethoxylate (C13) as corrosion inhibitor of mild steel in 1 M HCl through the use of the surface response methodology. A matrix of Doelhert to 4 factors was used as the experimental design in this research as it permits the use of the response surface methodology in a spherical field. The response used in the exploitation of the design was the determination of the inhibitor efficiency. It was assessed through gravimetric measurements on samples in the absence and presence of the inhibitor. The results were confirmed using electrochemical impedance spectroscopy (EIS).