L. Freire

Microstructural changes in a cementitious membrane due to the application of a DC electric field

The use of electromigration techniques to accelerate chloride ions motion is commonly employed to characterise the permeability of cementitious samples to chlorides, a relevant parameter in reinforced concrete corrosion. This paper is devoted to the study of microstructures changes occurring in mortar samples when submitted to natural diffusion and migration experiments. The application of an electric field reduces testing time in about one order of magnitude with respect to natural diffusion experiments. Nevertheless, the final samples microstructure differs in both tests. Impedance Spectroscopy is employed for real time monitoring of microstructural changes. During migration experiments the global impedance undergoes important increase in shorter period of time compared to natural diffusion tests. So, the forced motion of ions through the concrete membrane induces significant variations in the porous structure, as confirmed by Mercury Intrusion Porosimetry. After migration experiments, an important increase in the capillary pore size (10–100 nm) was detected. Conversely, no relevant variations are found after natural diffusion tests. Results presented in this work cast doubt on the significance of diffusion coefficient values obtained under accelerated conditions.

Oxide film growth by CSV on AISI 316L: a combined electrochemical and analytical characterization

The composition of the oxide layers formed in stainless steels is fundamental in the corrosion behavior of these materials. Its characterization has been widely studied, but still many questions arise, especially mechanisms of oxide growth and changes in its composition during the film development. This work aimed to study the chemical composition and electrochemical behavior of these films formed in different conditions of substrates de AISI 316L. The work investigated the effect of the number of cycles, scan rate, electrolyte composition and pH in the electrochemical response of the formed oxides. The increase of the scan rate promoted the formation of thinner films, richer in Fe3+ species, mainly hydroxide, with decreased conductivity. The study revealed a pH-dependent film composition, films formed in near neutral solutions presented higher resistivity and higher content of Fe species and traces of Mo compared to films formed in alkaline medium.

Electrochemical behaviour of Iron in chlorinated alkaline media: the effect of slurries from granite processing

Porrino is a well known zone of quarry and stone working of the SW of Galicia, Spain. In granites working processes 3 × 105 ton year-1 of granite powder are generated in this area, causing an important environmental problem. This dust has proved to be an efficient addition to high-strength concrete to improve mechanical properties. Nevertheless, no works have been published concerning the effect of this admixture in the passivation of steel reinforcements. The objective of the present work is to analyze the electrochemical behaviour of iron and carbon steel electrodes in alkaline solutions resulting from these slurries. The growth and evolution of the passive layers formed on the tested electrodes are studied by Cyclic Voltammetry and Electrochemical Impedance Spectroscopy. Scanning Electron Microscopy and X-ray powder Diffraction have been used for the morphological and chemical characterisation of the generated passive films. The effect of the presence of Cl- ions is also considered.

The effect of Al3+ in the passivity of iron in alkaline media containing chlorides

Abstract The behaviour of iron in alkaline media containing chlorides is studied in presence and absence of aluminate anions. The presence of aluminium in solution inhibits pitting of iron at least up to Cl− to OH− ratio equal to 5. This effect is due to lower cathodic reactivity.