0000000000476668
AUTHOR
C. Allely
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.
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…
Cut-edge corrosion of a Zn–55Al-coated steel: A comparison between sulphate and chloride solutions
Abstract Ex situ observations and in situ measurements of current and pH distributions over cut-edge coated steels revealed that Zn–55Al coatings are sacrificial only in chloride solutions, because of an activation of both Zn- and Al-rich phases present in the coating. In sulphate solutions, an efficient cathodic protection occurs only for short times of immersion, because only Zn-rich phases are active in this medium. The low solubility and strong acidification induced by Al(OH)SO4 allows only short distance cathodic protection, but cannot prevent red rust precipitation on the steel surface.
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 …
In situ investigation of sacrificial behaviour of hot dipped AlSi coating in sulphate and chloride solutions
Abstract The electrochemical behaviour of the cut-edge of hot-dipped aluminium–silicon-based alloy coated steel is studied in immersed conditions in sulphate and in chloride media. Preliminary studies performed on steel-pure Al bi-electrode demonstrate that a significant galvanic current can develop at short times (t