Abstract
The aqueous extract of the Helichrysum italicum leaves (HI) is tested as a corrosion inhibitor of an iron in a simulated acid rain using potentiodynamic polarisation, cyclic voltammetry and electrochemical impedance spectroscopy. Results of all electrochemical methods indicate an increase of a corrosion inhibition efficiency of the iron with the HI extract concentration. Maximum inhibition efficiency (~ 50 %) is obtained at 2.0 g L–1 HI extract. The inhibitive action is assumed to occur via an adsorption of the HI extract on the iron surface. Results indicate that the adsorption process is spontaneous and follows the Freundlich adsorption isotherm. According to the calculated ΔG value (~ 15 kJ mol–1), the corrosion inhibition of the iron occurs predominantly via a physisorption of the HI extract. The concentration of iron ions released into a solution, measured by atomic absorption spectrometry, is in accordance with the electrochemical results.
Highlights
I RON and stainless steel are among the most important materials because of their good properties and wide applications.[1,2,3] The main limitation for their applications is a corrosion attack.[4,5,6,7] The corrosion behaviour of metals and alloys primarily depends on the properties of the surface oxide layer
It is generally accepted that the passive film on the iron consists basically of a Fe(III) layer[4,6,7] and a good corrosion resistance of stainless steels lies in their ability to form a chromium-rich protective oxide layer, commonly called a passive film.[5,8]
The protection efficiency of the Helichrysum italicum leaves (HI) extract was increased with increasing its concentration, showing maximal efficiency around 50 % at 2 g L–1
Summary
I RON and stainless steel are among the most important materials because of their good properties and wide applications.[1,2,3] The main limitation for their applications is a corrosion attack.[4,5,6,7] The corrosion behaviour of metals and alloys primarily depends on the properties of the surface oxide layer. In industrial environments the corrosion occurs quite rapidly due to highly corrosive nature of airborne pollutants (oxides of nitrogen, sulphur and carbon). These oxides in contact with water in the atmosphere cause a formation of an acid rain (sulphuric and nitric acids) and promote the corrosion.[13,14,15,16,17] A rainfall with pH < 5.6 is considered the acid rain. In acid solution the corrosion inhibition of metals occurs through: electrostatic interaction of protonated molecules with already adsorbed ions, donor-acceptor interactions between π-electrons of aromatic ring and vacant d orbital of the surface iron atoms and interactions between unshared electron pairs of hetero atoms and vacant d-orbital of iron surface atoms.[9]
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