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.

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Abstract. The behavior of E400 steel, a constructional steel widely used in Senegal, was studied in aqueous NaCl solution in the presence of two types of clay: volcanic tuffs, and sedimentary montmorillonite. The protection efficiency of these compounds were electrochemically assessed (corrosion potential variation curves, polarization curves and electrochemical impedance spectroscopy) at various inhibitor contents. The results obtained showed that these inhibitors present an inhibitory efficacy of about 70% for an optimal concentration of 0.60% for the tuffs and 62% for a maximum content of 0.50% for montmorillonite.

Natural and aromatic substances contained in plants which can be extracted by hydro-distillation or by cold extraction, more commonly known as essential oils are used today in several fields including cosmetic, perfumery, food processing, traditional medicine, agriculture etc. More recently, a strong use of these products extracted from plants as a corrosion inhibitor of metals and alloys in an acidic environment has been observed, given the number of works that have been published in recent decades. This review represents a general study on essential oils for a better understanding of these natural products, but also a non-exhaustive study of the published research works on the use of essential oils as a corrosion inhibitor of metals and alloys, in particular mild steels in acidic environments. Most of these studies have revealed great potentials of essential oils in inhibiting the corrosion of metals in aggressive environment, such as acidic environment. Thus, they have proposed alternatives to artificial metal corrosion inhibitor known to cause environmental pollution and public health issues. This review is a contribution to research efforts carried out by scientific community to find green corrosion inhibitors. It lays the basis for future research work aimed to investigate on the corrosion inhibition properties of essential oils extracted from Senegalese local plants.

Synthetic compounds certainly exhibit good anticorrosive activity but also toxicity for humans and their environment. Because of these concerns, we turned to more environmentally friendly substances such as essential oils and of course other types of plant extracts. These products are considered green corrosion inhibitors. In this present study, we propose to make a comparative study of the inhibitory effect of extracts of two different essential oils, Eucalyptus camaldulensis (EC) and Cyperus rotundus (CR) on the corrosion of structural steel S235 in the medium 1 M hydrochloric acid. This inhibitory action was studied using potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The GC-MS analysis of the essential oils extracts showed that EC contains 96.2% oxygenated terpenes (90.6% monoterpenes and 5.6% sesquiterpenes), whereas CR includes 78.1% oxygenated terpenes (70.6% sesquiterpenes and 7.5% monoterpenes). Polarization measurements indicate that EC and CR are mixed inhibitors. The experimental results gave an inhibition efficiency close to 78.9% for EC and 86.7% for CR for an inhibitor concentration of 4 gL -1 at 293 K. The inhibition performances of these essential oils were correlated with their composition. The adsorption of the molecules of the oils responsible for the inhibition on the surface of the steel, in the hydrochloric acid solution, obeys the Langmuir adsorption isotherm. This present work has therefore shown that these two types of essential oils have a good inhibitory effectiveness on the corrosion of the metal S235 in 1M hydrochloric acid solution.