Bernard Tribollet

Corrosion of Pure Aluminium in Organic Acid Media in the Presence and in the Absence of Chloride Ions: Mass Transport Effects

The influence of mass transport on the corrosion behaviour of pure aluminium in 0.75% citric acid solution in the presence and in the absence of 104 ppm of chloride ions under anodic and cathodic polarisation was investigated with a rotating disk electrode and using electrochemical impedance spectroscopy. For anodically polarised electrodes, the impedance diagrams are composed of a high frequency (HF) capacitive loop followed by a low frequency (LF) inductive loop, whose shape and size are modified neither with immersion time nor with rotation speed. Addition of chloride ions causes a diminution of the diameter of the HF capacitive loop while the influence on the inductive loop cannot be clearly detected due to data scattering. Under conditions of cathodic polarisation, the diagrams present the shape described above, however, the diameter of both loops decreases with immersion time and electrode rotation speed.

Propriétés de l’interface d’infrastructures métalliques portuaires : facteurs d’impact corrosion/anticorrosion

Resume : L’exposition d’aciers a des conditions maritimes portuaires (immersion, marnage, eclaboussures...) conduit rapidement a la formation d’un depot sur la surface metallique Ce depot est constitue d’un melange de produits de corrosion de l’acier et de composes mineraux et organiques. La presence de ces depots peut se reveler protectrice ou nefaste vis-a-vis des phenomenes de corrosion selon leurs caracteristiques (nature, repartition, conductivite, ...). Cette etude vise a ameliorer les connaissances des proprietes d’interfaces acier/environnement des infrastructures metalliques portuaires afin d’optimiser la mise en place et le dimensionnement d’un systeme de protection cathodique. Ces travaux sont bases sur l’analyse des caracteristiques physico-chimiques et electrochimiques des depots formes sur des coupons d’acier au carbone exposes 6 a 7 ans en zone des basses eaux en conditions naturelles portuaires au sein des Grands Ports Maritime de NantesSaint-Nazaire et du Havre. Ces coupons ont ete places dans differentes conditions d’essais : sous protection cathodique permanente ou differee, a l’abandon ou sous rupture de protection. Les resultats de ce travail de recherche a permis de mettre en evidence, quel que soit le site pilote (estuarien ou strictement maritime), la formation de produits de corrosion selon le mecanisme generalement attendu sur des coupons d’acier a l’abandon. La protection cathodique permet une diminution significative de la cinetique de corrosion. Elle ne modifie pas fondamentalement la nature des produits de corrosion mais favorise la formation d’un depot plus protecteur que celui obtenu a l’abandon. Mots cles : Corrosion marine – Protection cathodique – Electrochimie – Raman – DRX

Corrosion Study of Cast Iron Pipes in Water Distribution Systems by Impedance. Application to Chlorine Consumption

Among the various causes of chlorine consumption in potable water distribution networks, corrosion has not been so far seriously considered. This work focused on the corrosion study of cast iron, as a representative material of those networks, by both electrochemical methods -steady-sate curves, corrosion potential and ac impedance data- and classical photographs observations in the absence and in the presence of chlorine. A process model based on the de Levie theory is used to extract from the experimental impedance data, the value of the charge transfer resistance corresponding to the anodic reaction and by this way the corrosion rate. From impedance and photographs, a structure of the different corrosion layers has been proposed. The general conclusion is that chlorine is not directly consumed electrochemically at the metal though it is more easily reducible than oxygen. Thus, the total consumption of chlorine, induced by the corrosion of cast iron pipes, amounts to the chemical reduction due to ferrous ions released by the metal dissolution. Moreover the rate of chlorine decay is exactly obtained from the corrosion current density.