Corrosion in viewpoint of metal microstructure for grey and ductile cast iron in HCl solutions and presence of thiourea Online publication date: Sun, 07-Oct-2007
by Sayed S. Abd El Rehim, Sayed H. El-Nekhaly, Ahmed El Essawy Abdou
International Journal of Microstructure and Materials Properties (IJMMP), Vol. 2, No. 3/4, 2007
Abstract: Two types of cast iron were employed in this work. Grey cast iron was the first type, and ductile was the second one. Two specimens of the grey cast iron sample were used; one was kept without heat treatment, and the second was completely heat-treated by ferritisation regime. The two specimens of ductile cast iron were used similarly; one was kept without heat treatment grey and the second was ferritised by heat treatment. Potentiodynamic technique was applied for collecting corrosion data of the above four metal specimens in HCl solutions in the absence and presence of thiourea as an inhibitor. The measurements were performed in different concentrations of HCl (0.05, 0.2, 0.5, and 1 M) at 20ºC and in the absence of an inhibitor, on the other hand, corrosion parameters were collected in 0.2 M HCl at different temperature levels (20ºC, 30ºC, 40ºC, and 50ºC). Thiourea was added in different concentrations to 0.2 M HCl at 25ºC, then corrosion data was deduced. An optical microscope was used to investigate the microstructure of grey and ductile cast iron before and after heat treatment. Corrosion resistance and corrosion rates were collected directly from potentiostat, where Tafel lines were applied to the software. The above raw data was used to deduce activation thermodynamic parameters (Ea*, ΔHº, and ΔSº) of dissolution processes in the absence of thiourea by applying Arhenius equation. Adsorption parameters, in the presence of thiourea, were deduced using the kinetic model and the Flory-Huggins isotherms were used as inhibition mechanisms for the investigation before and after treatment.
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