Investigation of self-healing mechanism on galvanized steels cut edges by coupling SVET and numerical modeling
Local cathodic inhibition has been observed on the cut-edge of galvanized steel immersed in 0.03 M NaCl solution using the scanning vibrating electrode technique. The current distribution results indicate that cathodic inhibition occurs in a limited spatial zone located between the cathodic sites on the steel and the anodic sites on the exposed zinc surface. The experimental current distributions are compared with the results of numerical simulations that show the specific diagnostic features for the detection of cathodic inhibition from scanning vibrating electrode technique (SVET) data so as to distinguish the zero current regions from experimental artifacts due to the lateral resolution …
The anodic and cathodic dissolution of Al and Al–Cu–Mg alloy
Abstract Atomic emission spectroelectrochemistry (AESEC) was used to monitor the release of Al from 99.99% aluminum (1199 alloy) and Al, Mg, and Cu from 2024 Al alloy in 30 g/l NaCl electrolyte as a function of pH. The cathodic dissolution of Al was demonstrated and attributed to an increase in the pH at the interface due to the water reduction reaction. The dissolution of Mg was also observed but was a more complex function of current probably depending on the interfacial pH and the Al dissolution rate. The detachment of copper-rich particles was observed as very rapid spectroscopic emission transients (peak width
Predictive Model for Cut-Edge Corrosion of Galvanized Steels
A numerical model for the electrochemical behavior of cut-edge of galvanized steels is proposed. Some experimental data of current densities above cut-edge immersed in a 0.03M NaCl solution have been measured, using a scanning vibrating electrode technique, and compared with some simulated ones. A good fit has been obtained. The model geometry has been modified by decreasing the electrolyte thickness in order to tend towards an atmospheric corrosion case; such situation that is not easily accessible by electrochemical studies. Three regions can be distinguished according to the efficiency of the galvanic coupling to protect steel.
Impedance characterization of the electrochemical environment under a polymer film artificially delaminated
International audience; Knowledge of the electrical conductivity of the zone under a delaminated paint film is one necessary input parameter for the simulation of electrochemically driven underpaint corrosion. In this work, a microelectrode array system has been developed, tested, and applied to measure the spatial distribution of resistivity in the delaminated zone along the metal/polymer interface. The experimental device consists of a linear array of six 100 m diameter stainless steel microelectrodes (100 m in diameter) embedded in a steel substrate. A polymer coatingwas applied and an artificial "delaminated zone"was created using the laser-induced decohesion technique. The electrochemi…
Protective mechanisms occurring on zinc coated steel cut-edges in immersion conditions
Abstract Electrochemical processes occurring on the cut-edge of a galvanized steel immersed in NaCl solutions were studied using numerical simulations, and in situ current and pH profiles measured over the cut-edge. These results clearly demonstrate that only the steel surface remote from the zinc coating is cathodically active, oxygen reduction being strongly inhibited in the vicinity of zinc. This trend was confirmed by local polarization curves recorded on these distinct areas. Ex-situ AES and SEM analysis and cathodic polarization curves in solutions containing Zn 2+ ions led to conclude that this cathodic inhibition was related to the fast nucleation of a dense Zn(OH) 2 film on the ste…
Modeling bimetallic corrosion under thin electrolyte films
A finite element model (FEM) was developed to calculate the potential distribution in the electrolyte in the case of bimetallic corrosion between iron and zinc electrodes, taking into account mass transport of oxygen in the solution. This model was first compared with experimental results obtained by scanning vibrating electrode technique (SVET) on a galvanized steel cut-edge in immersion conditions in a 0.03 M NaCl electrolyte. A good agreement was obtained between the calculated and experimental current densities. The model predicted the evolution of the galvanic coupling as function of the electrolyte thickness and for various iron–zinc surface area ratios. Different coupling regimes wer…
Reliability of numerical models for simulating galvanic corrosion processes
International audience; Maturity of numerical simulation represents an important issue in the development of predictive models of galvanic corrosion. As widely used in electrochemical engineering, a coupled electrochemical-transport-reaction (CETR) model is recommended to simulate the current distribution above a galvanic corrosion cell made of the cut-edge of a galvanized steel sheet. Nevertheless, simulating current density distributions obtained experimentally by scanning vibrating electrode technique (SVET) above such a galvanic cell appears to be more accurate using an electrostatic model considering a homogeneous conductivity. In this case, the absence of concentration gradients next …
Influence of magnesium content on the corrosion resistance of the cut-edges of Zn–Mg-coated steel
Abstract The ability of Zn–Mg coatings (with magnesium content between 5.8 and 15.5 wt.%) to protect steel sheets has been evaluated with local electrochemical techniques (scanning vibrating electrode technique, microcapillary electrochemical cell) and rotating disk electrode, and compared with the corrosion protection afforded by a pure zinc coating. From immersion tests of coated steel cut-edges, it is observed that alloying zinc with magnesium leads to a decrease of the galvanic current between the coating and the steel surface, and to an improvement of the steel corrosion resistance after a drying period, due to the presence of magnesium in the corrosion products.