A study of Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana as eco-friendly corrosion inhibitors for 1018 carbon steel in 0.5 M H 2SO 4 has been carried out by using weight loss tests, potentiodynamic polarization curves and electrochemical impedance spectroscopy measuremnts. Results have shown that the three extracts performed as good corrosion inhibitors, but the Eruca vesicaria exhibited the best performance followed by Erythrina americana. The three inhibitors formed a protective, passive film which protected the steel from corrosion. This was because they contain antioxidants present in their molecular structure with heteroatoms such as N, C and O like phenols, amino acids, etc., which react with metal and environment to form the protective film.
Corrosion causes big economic looses to the industry and is a cause of big accidents. In industrial processes such as acid pickling, well oil acidizing, metals and alloys are exposed to corrosive environments such as sulfuric acid (H2SO4), hydrochloric acid (HCl) and phosphoric acid (H3PO4) among others, which causes corrosion [
Eruca vesicaria subsp. sativa (syn. E. sativa), Bromelia hemisphaerica and Erythrina americana are plants widely used in Mexico because they are excellent source of antioxidants, enzimes or sedative and calming effects [
Material tested in this work was 1018 carbon steel containing 0.14% C, 0.90% Mn, 0.30% S, 0.030% P and as balance Fe, encapsulated in commercial epoxic resin with an exposed area of 1.0 cm2. The aggressive solution, 0.5 M H2SO4 was prepared by dilution of analytical grade chemical in distilled water. Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana were obtained from a local market.For the extraction, dried leafs of the plants were soaked in methanol during 21 days obtaining a solid, which was weighted and dissolved in methanol and used as a stock solution and used then for preparation of the desired concentrations by dilution. Used concentrations included 0, 200, 400, 600, 800 and 1000 ppm. To characterize the obtained extracts, FTIR technique was used. The IR spectra were recorded with KBr pellets on a Tensor 27 Bruker spectrophotometer between 400 and 4000 cm−1. For the corrosion tests, both gravimetric and electrochemical techniques were used.
Weight loss experiments were carried out with carbon steel rods 2.5 cm length and 0.6 cm diameter abraded with fine emery paper until 1200 grade, rinsed with acetone, and exposed to the aggressive solution during 72 h. After a total time of exposition of 72 hours, specimens were taken out, washed with distilled water, degreased with acetone, dried and weighed accurately. Tests were performed by triplicate at room temperature (25˚C). Corrosion rates, in terms of weight loss measurements, DW, were calculated as follows:
where m1 is the mass of the specimen before corrosion, m2 the mass of the specimen after corrosion, and A the exposed area of the specimen. For the weight loss tests, inhibitor efficiency, I.E., was calculated as follows:
where DW1 is the weight loss without inhibitor, and DW2 the weight loss with inhibitor. Specimens were weighed in an analytical balance with a precision of 0.1 mg.
Electrochemical techniques employed included potentiodynamic polarization curves and electrochemical impedance spectroscopy measurements, EIS. In all experiments, the carbon steel electrode was allowed to reach a stable open circuit potential value, Ecorr. Polarization curves were recorded at a constant sweep rate of 1 mV/s at the interval from −1000 to +1000 mV respect to the Ecorr value. Measurements were obtained by using a conventional three electrodes glass cell with two graphite electrodes symmetrically distributed and a saturated calomel electrode (SCE) as reference. Corrosion current density values, icorr, were obtained by using Tafel extrapolation. Electrochemical impedance spectroscopy tests were carried out at Ecorr by using a signal with an amplitude of 10 mV in a frequency interval of 100 mHz - 20 kHz. An ACM potentiostat controlled by a desk top computer was used for the polarization curves, whereas for the EIS measurements, a model PC4 300 Gamry potentiostat was used.
The effect of Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana concentration on the weight loss of 1018 carbon steel in 0.5 M H2SO4 is shown in
The effect of Eruca vesicaria concentration in the polarization curves for 1018 carbon steel in 0.5 M H2SO4 is given in
The Ecorr value shifts towards nobler values as soon as the Eruca vesicaria is added to the solution, and the icorr values decrease with the addition of the inhibitor for one order of magnitude up to 800 ppm,
Cinh (ppm) | Ecorr (mV) | icorr (mA/cm2) | βa (mV/dec) | βc (mV/dec) | I.E. (%) | Epas (mV) | ipas (mA/cm2) |
---|---|---|---|---|---|---|---|
0 | −426 | 1.94 × 10−4 | 36 | 177 | --- | 680 | 7.8 × 10−4 |
200 | −384 | 3.5 × 10−5 | 27 | 142 | 82 | 536 | 5.94 × 10−4 |
400 | −384 | 3.1 × 10−5 | 24 | 136 | 84 | 535 | 3.94 × 10−4 |
600 | −403 | 2.63 × 10−5 | 22 | 131 | 86 | 678 | 2.44 × 10−4 |
800 | −424 | 1.9 × 10−5 | 21 | 122 | 90 | 760 | 7.64 × 10−5 |
1000 | −356 | 2.8 × 10−5 | 20 | 120 | 65 | -- | 8.74 × 10−5 |
Epas, as well as the passive current density value, ipas, were decreased with the addition of Eruca vesicaria, indicating that a better passive film is formed on top of steel when Eruca vesicaria is present. Thus, Eruca vesicaria helps to improve the passive film properties of the steel.
Polarization curves for 1018 carbon steel at different concentrations of Bromelia hemisphaerica is shown in
Finally, the effect of Erythrina americana concentration on the polarization curves for 1018 carbon steel in 0.5 M H2SO4 is shown in
Cinh (ppm) | Ecorr (mV) | icorr (mA/cm2) | βa (mV/dec) | βc (mV/dec) | I.E. (%) | Epas (mV) | ipas (mA/cm2) |
---|---|---|---|---|---|---|---|
0 | −426 | 1.94 × 10−4 | 36 | 177 | --- | 680 | 7.8 × 10−4 |
200 | −414 | 7.1 × 10−5 | 34 | 155 | 64 | 530 | 5.94 × 10−4 |
400 | −394 | 7.4 × 10−5 | 32 | 146 | 62 | 635 | 4 × 10−4 |
600 | −416 | 6.7 × 10−5 | 30 | 134 | 65 | 615 | 2.94 × 10−4 |
800 | −431 | 5.0 × 10−5 | 29 | 128 | 74 | 570 | 1 × 10−4 |
1000 | −407 | 6.8 × 10−5 | 20 | 123 | 65 | 570 | 2.54 × 10−4 |
Cinh (ppm) | Ecorr (mV) | icorr (mA/cm2) | βa (mV/dec) | βc (mV/dec) | I.E. (%) | Epas (mV) | ipas (mA/cm2) |
---|---|---|---|---|---|---|---|
0 | −426 | 1.94 × 10−4 | 36 | 177 | --- | 680 | 7.8 × 10−4 |
200 | −403 | 3.5 × 10−5 | 32 | 136 | 82 | 530 | 3.7 × 10−4 |
400 | −400 | 3.0 × 10−5 | 24 | 138 | 84 | 735 | 4.6 × 10−5 |
600 | −384 | 6.3 × 10−5 | 58 | 131 | 67 | 678 | 6.54 × 10−5 |
800 | −403 | 3.9 × 10−5 | 24 | 172 | 79 | 640 | 4.94 × 10−5 |
1000 | −385 | 7.1 × 10−5 | 36 | 170 | 63 | 670 | 8.34 × 10−5 |
highest value, 84%, at 400 ppm of Erythrina americana, value slightly lower than the highest efficiency obtained with Eruca vesicaria, 90%. Both anodic and cathodic Tafel slopes were lowered by the addition of Erythrina americana, indicating that it acts as a mixed type of inhibitor, decreasing both the anodic iron dissolution and cathodic hydrogen evolution reactions. The Epas value was lowered only with the addition of 200 ppm of Erythrina americana, whereas the passive current density value, ipas, was lowered by the addition of 200, 800 and 1000 ppm of Erythrina americana, forming, at these concentrations, a better passive film on top of the steel, improving, thus, the film passive properties.
The effect of Eruca vesicaria concentration in the Nyquist diagrams for 1018 carbon steel in 0.5 M H2SO4 is given in
Cinh (ppm) | Rs (Ohm cm2) | Rct (Ohm cm2) | Cdl (F/cm2) | I.E. (%) |
---|---|---|---|---|
0 | 1.7 | 46 | 8.5 × 10−5 | --- |
200 | 1.8 | 214 | 3.7 × 10−5 | 78 |
400 | 3.6 | 298 | 3.3 × 10−5 | 84 |
600 | 2.4 | 386 | 2.6 × 10−5 | 88 |
800 | 2.4 | 731 | 2.4 × 10−5 | 93 |
1000 | 1.8 | 314 | 3.5 × 10−5 | 85 |
surface, displacing the water molecules from the steel surface.
Nyquist diagrams for 1018 carbon steel at different concentrations of Bromelia hemisphaerica is shown in
The effect of the three extracts concentration on the Rct values for 1018 carbon steel in 0.5 M H2SO4 is shown in
It is generally accepted that the first step during the adsorption of an organic inhibitor on a metal surface usually involves replacement of water molecules absorbed on the metal surface:
The inhibitor may then combine with freshly generated Fe2+ ions on steel surface, forming metal inhibitor complexes [
The resulting complex, depending on its relative solubility, can either inhibit or catalyze further metal dissolution. At low concentrations the amount of inhibitor is not enough to form a compact complex with the metal
ions, so that the resulting adsorbed intermediate will be readily soluble in the acidic environment. But at relatively higher inhibitor concentrations, more inhibitor molecules become available for the complex formation, which subsequently diminishes the solubility of the surface layer, leading to improve the inhibition of metal corrosion. Thus, it has been shown that the decrease in icorr and the increase in the Rct values is due to the protective character of the inhibitors. Micrographs of corroded surfaces after being corroded in H2SO4 shown in
film formed on top of steel, which gives some protection to the steel as evidenced by polarization curves in
The good corrosion inhibition properties shown by Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana is due to the presence of antioxidants present in their molecular structure containing heteroatoms such as N, C and O. For instance, Eruca vesicaria and Erythrina americana contain amino acids, and phenols. Infrared diagram for the pure Eruca vesicaria, 0.5 M H2SO4 + 800 ppm of Eruca vesicaria before and after the polarization curve are shown in
Wave number (cm−1) | Assigned functional group |
---|---|
3340 | O-H |
2900 | NH2 |
1740 | C=O |
1050 | C-O |
It has been shown that Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana acted as good corrosion inhibitors for 1018 carbon steel in 0.5 M H2SO4, with the best efficiency exhibited by Eruca vesicaria, 80%, whereas the worst efficiency, 40%, was exhibited by Bromelia hemisphaerica. The three inhibitors improved the protective properties of the formed passive film on top of the steel by reducing both the passivation potential and current density values. The protection given by the different extracts is due to the presence of antioxidants like phenols and amino acids, which contain heteroatoms in their structure such as C, N, or O, which react with metal and environment to form a complex which adsorbs on to the steel and protect it from the environment.
M. J.Garcia-Ramirez,G. F.Dominguez Patiño,J. G.Gonzalez-Rodriguez,M. L.Dominguez-Patiño,J. A.Dominguez-Patiño, (2016) A Study of Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana as Green Corrosion Inhibitors for Carbon Steel in Sulfuric Acid. Advances in Materials Physics and Chemistry,06,9-20. doi: 10.4236/ampc.2016.62002