Journal of Materials Research and Technology Journal of Materials Research and Technology
J Mater Res Technol 2018;7:231-9 DOI: 10.1016/j.jmrt.2017.07.004
Original Article
Corrosion behaviour of S43035 ferritic stainless steel in hot sulphate/chloride solution
Roland Tolulope Lotoa,, , Cleophas Akintoye Lotoa,b
a Department of Mechanical Engineering, Covenant University, Ota, Ogun State, Nigeria
b Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, South Africa
Received 27 April 2017, Accepted 04 July 2017
Abstract

The corrosion resistance of S43035 ferritic stainless steel at elevated temperatures of 308K, 328K, 348K and 378K was studied through potentiodynamic polarization test and optical microscopy analysis in 2M H2SO4 at 0%, 1%, 3.5% and 6% NaCl. Results show that increase in temperature and NaCl generally hinders the formation of the passive film. Changes in corrosion rate from 308K to 378K at 0% NaCl was marginal. Metastable pitting was absent until 378K due to increased electrolytic action of SO42− ions. In the presence of chlorides at 308K metastable pitting is visible delaying the formation of stable passive film. Passivation behaviour was absent at temperatures above 308K due to polarization similar to carbon steels and a strong decrease in hydrogen evolution over potential especially at 1% and 3.5% NaCl. Optical images showed mild deterioration at 378K from 0% NaCl and the formation of corrosion pits at 308K and 378K from 6% NaCl. Negative enthalpy value at 0% NaCl implies exothermic nature of the steel corrosion reaction. Addition of chlorides changed the steel corrosion reaction to endothermic. Increase in NaCl concentration caused a decrease in activation energy and increase in entropy values due to decrease in passivation of the alloy and consequently increase in corrosion rate. Statistical analysis through ANOVA at confidence levels of 95% and 97.5% showed the strong influence of temperature variation on corrosion rate with F-values of 5.256 at 50.8% in contrast to the NaCl concentration whose value was below the significance level.

Keywords
Corrosion, Ferritic, Sulfuric, Steel, NaCl, Passivation
J Mater Res Technol 2018;7:231-9 DOI: 10.1016/j.jmrt.2017.07.004
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