Ezzeddine Triki

Influence of Phosphate on Corrosion Products of Iron in Chloride-Polluted-Concrete-Simulating Solutions: Ferrihydrite vs Green Rust

Abstract The corrosion of steel-reinforcing bar (rebar) in concrete induced by the diffusion of chloride ions was simulated with a-iron foils dipped in various aqueous electrolytes. Sodium chloride (NaCl) was added to saturated calcium hydroxide (Ca[OH]2) solutions to simulate concrete polluted with chloride ions whereas solutions containing sodium bicarbonate (NaHCO3), sodium carbonate (Na2CO3), and NaCl were used as carbonate- and chloride-containing concrete. The corrosion process was electrochemically induced by cyclic voltammetry and galvanostatic methods. Similar experiments were performed with solutions where various amounts of trisodium phosphate (Na3PO4) were added. The galvanostatic potential dropped to ∼ −0.15 V vs standard hydrogen electrode (SHE) in the absence of phosphate, indicating that active corrosion took place, while it reached values of ∼1 VSHE with large phosphate concentrations. The corrosion products were analyzed by Mossbauer spectroscopy. They mainly consisted of iron(II) compou...

Study of Zn-Ni Alloy Coatings Modified by Nano-SiO2 Particles Incorporation

The aim of this research work was to codeposit nano-SiO2 particles into Zn-Ni alloy coatings in order to improve some surface properties. It had been investigated the effect of loading the plating bath with nanoparticles on composition, morphology, phase structure of deposits, and their subsequent influence on the corrosion process in corrosive solution of 3% NaCl and the thermal stability of deposits at C. It was found that Zn-Ni alloy composites contain a higher percentage of Ni with incorporation in the deposit of 1.54% of silica. X-ray diffraction measurements revealed that the alloys consisted of two phases, pure zinc and phase. Electrochemical characterization of the composites had been carried out through potentiodynamic polarization and electrochemical impedance spectroscopy. The composites exhibited higher values of microhardness and better corrosion resistance in corrosive media.

Adsorption of corrosion inhibitors (SA, HEDP) using EQCM: chloride effect and synergic behavior

The adsorption of inhibitor molecules, ascorbic acid (SA), and 1-hydroxyethane-1,1-diphosphonic acid (HEDP), was studied using electrochemical quartz crystal microbalance. Adsorption on iron was studied compared with gold in the presence of chloride ions and at EOP and cathodic potential. Each of these parameters significantly affects monolayer adsorption following the Langmuir isotherm. HEDP was adsorbed more rapidly than SA. The novelty in this study concerns the influence of chloride concentration on the inhibition efficiency. Indeed, the rate of inhibition also depends on the concentration ratio of chloride/inhibitor, which is an important factor for the practical implementation of these compounds. Adding a small quantity of chloride ions can increase adsorption rate as well as degree of coverage. Optimum behavior was noted for a HEDP/Cl− ratio about 500. Passivation of the electrode to cathodic potential influenced HEDP adsorption and promoted that of SA. A low adsorption current proportional to the concentration of the inhibitor was recorded. A synergic inhibition by the two molecules was observed for a concentration relationship of 1.16. The study showed that SA was not adsorbed at the interface but its presence made a reduction in lateral tensions possible between adsorbed HEDP, leading to a better coverage.