Carob seed oil: an efficient inhibitor of C38 steel corrosion in hydrochloric acid

Dris Ben Hmamou Rachid Salghi Abdelkader Zarrouk Omar Benali Fatiha Fadel Hassan Zarrok Belkheir Hammouti Background: The carob seed oil (CO) was tested as inhibitor of the corrosion of C38 steel in 1 M HCl by weight loss and electrochemical measurements. The extract was found to inhibit the corrosion of C38 steel in 1 M HCl. Results: The results of the study reveal that the inhibition efficiency of CO depends on its concentration and attains approximately 86.7% at 0.5 g/L. Polarization curves reveal that CO is a mixed-type inhibitor. Changes in impedance parameters (charge transfer resistance, Rt, and double-layer capacitance, Cdl) were indicative of CO adsorption on the metal surface, leading to the formation of a protective film. The effect of temperature on the corrosion behavior with the addition of 0.5 g/L of carob seed oil was studied in the temperature range of 298 to 328 K. Conclusions: Results show that the inhibition efficiency of the plant extract increases with increasing temperature, and the adsorption of the latter on the C38 steel surface is found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution processes were also determined. - Background Acid solutions generally used for the removal of rust and scale in industrial processes and the deterioration of metal due to these processes are very significant. Inhibitors are used in these processes to control metal dissolution. Hydrochloric acid is widely used in the pickling of steel and different steel-based alloys [1,2]. One way of protecting steel from corrosion is to use corrosion inhibitors. Organic compounds containing heteroatoms are commonly used to reduce the corrosion attack on steel in acidic media [3-16]. The recent trend is towards environmentally friendly inhibitors. Most of the natural products are non-toxic, biodegradable, and readily available in plenty. These advantages have incited us to draw a large part of our laboratory program to examine natural substances as corrosion inhibitors such as fennel oil [17], prickly pear seed oil [18], argan extract [18-21], argan oil [19,22], rosemary oil [23-25], Thymus oil * Correspondence: 1Equipe de Gnie de l'Environnement et de Biotechnologie, ENSA, Universit Ibn Zohr, BP 1136, Agadir 8000, Morocco Full list of author information is available at the end of the article [26,27], pennyroyal mint oil [28], lavender oil [29], jojoba oil [30], and Artemisia [31-33]. Carob fruits are among the most import tree fruit crops in the Mediterranean countries, and their production and consumption have increased considerably in recent years. They are widely used in the boiled juice pekmez production and powder drink industry. The seeds of the carob are utilized in the food industry for their gum content [34]. The present work was established to study the corrosion inhibition of C38 steel in 1 M HCl solution by carob seed oil as corrosion inhibitor using different techniques: weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Methods Fatty acid composition The fatty acid composition was determined following the ISO standard ISO 5509:2000 (ISO 2000) [35]. In brief, one drop of the oil was dissolved in 1 mL of nheptane, 50 g of sodium methylate was added, and the closed tube was agitated vigorously for 1 min at room temperature. After adding 100 L of water, the tube was centrifuged at 4,500g for 10 min, and the lower aqueous phase was removed. Then, 50 L of HCl (1 mol with methyl orange) was added, the solution was shortly mixed, and the lower aqueous phase was rejected. About 20 mg of sodium hydrogen sulfate (monohydrate, extra pure; Merck, Darmstadt, Germany) was added, and after centrifugation at 4,500g for 10 min, the top n-heptane phase was transferred to a vial and injected in an Agilent Technologies 6890 N gas chromatograph equipped with a capillary column (30 m 0.32 mm; Supelco, Bellefonte, PA, USA) and flame ionization detection. The column was programmed to increase from 135C to 160C at 2C/min and from 160C to 205C at 1.5C/min; the detection temperature was maintained at 220C, injector temperature 220C. The vector gas was helium at a pressure of 5,520 Pa. Peaks were identified by comparing retention times with those of standard fatty acid methyl esters. Weight loss measurements Coupons cut into 2 cm 2 cm 0.08 cm dimensions (having composition of 0.179% C, 0.165% Si, 0.439% Mn, 0.203% Cu, 0.034% S, and Fe balance) are used for weight loss measurements. Prior to all measurements, the exposed area was mechanically abraded with 180, 320, 800, and 1,200 grades of emery papers. The specimens are washed thoroughly with bidistilled water, degreased, and dried with ethanol. Gravimetric measurements are carried out in a double-walled glass cell equipped with a thermostated cooling condenser. The solution volume is 80 cm3. The immersion time for the weight loss is 6 h at 298 K. Electrochemical tests The electrochemical study was carried out using a potentiostat PGZ100 piloted by Voltamaster software. This potentiostat is connected to a cell with three electrode thermostats with double wall (Tacussel Standard CEC/TH). A saturated calomel electrode and platinum electrode were used as reference and auxiliary electrodes, respectively. The material used for constructing the working electrode was the same with that used for the gravimetric measurements. The surface area exposed to 2 the electrolyte is 0.04 cm . Potentiodynamic polarization curves were plotted at a polarization scan rate of 0.5 mV/s. Before all experiments, the potential was stabilized at free potential during 30 min. The polarization curves are obtained from 800 to 400 mV at 298 K. The solution test is thereafter de-aerated by bubbling nitrogen. Gas bubbling is maintained prior and throughout the experiments. In order to investigate the effects of temperature and immersion time on the inhibitor performance, some tests were carried out in a temperature range of 298 to 328 K. The EIS measurements are carried out with the electrochemical system (Tacussel), which included a digital potentiostat model Voltalab PGZ100 computer (Radiometer Analytical, Lyon, France) at Ecorr after immersion in solution without bubbling. After the determination of steady-state current at a corrosion potential, sine wave voltage (10 mV) peak to peak at frequencies between 100 kHz and 10 mHz are superimposed on the rest potential. Computer programs automatically controlled the measurements performed at rest potentials after 0.5 h of exposure at 298 K. The impedance diagrams are given in the Nyquist representation. Experiments are repeated three times to ensure the reproducibility. Inhibition efficiencies EI% were calculated as follows: where Wc0orr andWcorrare the corrosion rates of steel due to the dissolution in 1 M HCl in the absence and the presence of definite concentrations of the inhibitor, respectively. For impedance measurements: wher (...truncated)