Abstract
The corrosion behavior of three constructional steels used in Senegal, S235, S275 and S355, was studied in simulated atmospheric conditions in an exposure chamber above distilled water and above 3% NaCl solution representing marine atmosphere by comparing the ratio of rusted to unrusted area. Electrochemical test methods (potentiodynamic tests and electrochemical impedance spectroscopy) were employed to study the steels fully immersed in acidic, near neutral and basic conditions in 0.5 M HCl, NaCl, and NaOH solutions, respectively. Results indicate that S355 and S235 steels have comparable corrosion resistance, which are much lower than that of S275. KEY WORDS: Corrosion, Steel, Salt spray, Tafel polarization, Electrochemical impedance spectroscopy Bull. Chem. Soc. Ethiop. 2015, 29(2), 299-310DOI: http://dx.doi.org/10.4314/bcse.v29i2.12
Highlights
Steel is an alloy used in construction and mechanical engineering
In order to assess the impact of salt on the atmospheric corrosion of the studied materials, plots of the corrosion ratios evolution with time (Figure 3-B), the steels being exposed above 3% aqueous solution of NaCl solution and above distilled water (Figure 3-A) are presented for comparison
As a large charge-transfer resistance is associated with a slower corroding system [32], these results confirm that S235 is less corrosion resistant than S355
Summary
Steel is an alloy used in construction and mechanical engineering. Steels are necessary in almost all the fields that require technical application. The corrosion behavior of the steels were studied using two methods; surface analysis for simulated atmospheric tests and electrochemical tests (potentiodynamic and electrochemical impedance spectroscopy), for samples immersed in aqueous media. Atmospheric corrosion rates were evaluated on samples put in a controlled atmosphere"exposure chamber" The atmosphere in this chamber is saturated with humidity provided either by distilled water (this type of atmosphere is referred to as humid atmosphere) or by aqueous sodium chloride and hermetically closed. Before running any EIS measurement, the working electrode was held at its open circuit potential for an equilibrium time of 30 min to obtain a steady state Both electrochemical techniques were repeated twice on each sample and the average value was reported
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